A brief examination of the usage of "His servants" or "My Servants" in the book of Revelation. Just who is being referred to by this phrase?
His Servants
(Rev 1:1) The Revelation of Jesus Christ, which God gave unto him, to shew unto his servants things which must shortly come to pass; and he sent and signified it by his angel unto his servant John:

This verse ties the "John" class to the remainder of "his servants," showing that the "John" class is both a part of and yet is treated separately from "his servants." The "John" class is the church in the flesh during "the Lord's day" (i.e., from 1874 until the last member of the Body of Christ finishes their earthly course.) - Please see Additional Comments for Rev. 1:10 concerning the identification of the John class.

(Rev 2:20) Notwithstanding I have a few things against thee, because thou sufferest that woman Jezebel, which calleth herself a prophetess, to teach and to seduce my servants to commit fornication, and to eat things sacrificed unto idols.

This is set during the Fourth stage of the church (Thyatira - Messenger: Peter Waldo, beginning about 1160 A.D.) The false (Catholic) church is accused of seducing "my servants" to join her in accepting this practice of being united to a King other than her True King Jesus. This other king was the state, whose civil power rested in the king.
(Rev 7:3) Saying, Hurt not the earth, neither the sea, nor the trees, till we have sealed the servants of our God in their foreheads.

The servants of God are the 144,000 who are sealed in the forehead. This cannot include the Great Company for they are described separately in vss. 9-17
(Rev 19:2) For true and righteous are his judgments: for he hath judged the great whore, which did corrupt the earth with her fornication, and hath avenged the blood of his servants at her hand.

The Great Company is here speaking and declaring that God has indeed avenged the blood of "his servants" at the hand of the great whore. This is a clear reference to Rev. 6:9-10 where we find "the souls of them that were slain for the word of God..." crying out and asking how long until "thou dost not judge and avenge our blood". Clearly these who are crying out are the saints. The description of these that they "were slain for the word of God" is almost the same language as that of Rev. 20:4 which describes those who are to live and reign with Christ a thousand years, i.e., the church, the 144,000. Thus, "his servants" refers to the saints.
(Rev 19:5) And a voice came out of the throne, saying, Praise our God, all ye his servants, and ye that fear him, both small and great.

At first it seemed as though this verse might be the exception because it includes those 'that fear him, both small and great.' However, we cannot ignore the word 'AND.' 'Praise our God, all ye his servants, and ye that fear him, both small and great.' The word 'and' places 'His Servants' into a different group from those described as the 'small and great' that fear him.
Rev 22:3-4 And there shall be no more curse: but the throne of God and of the Lamb shall be in it; and his servants shall serve him: [4] And they shall see his face; and his name shall be in their foreheads.
This makes it absolutely clear. It can only be the Little Flock that is here referred to because of two characteristics.
1. They see His face. Spirit born can see His face.
2. These have his name in their foreheads. - True of the 144,000 - see Rev. 14:1
One verse mentions Two groups of 'Servants'
(Rev 22:6) And he said unto me, These sayings are faithful and true: and the Lord God of the holy prophets sent his angel to shew unto his servants the things which must shortly be done.

This verse makes it clear that 'His Servants' and 'His Servants the Prophets' are two distinct groups.
It points us back to Rev. 1:1 where "his servants" were shown, in sign language, the things to come by "his angel" (Pastor Russell).
So, the next obvious question is: Who are 'His Servants the Prophets?'
His Servants the Prophets

2 Kings 9:7 And thou shalt smite the house of Ahab thy master, that I may avenge the blood of my servants the prophets, and the blood of all the servants of the LORD, at the hand of Jezebel. (Rev 10:7) But in the days of the voice of the seventh angel, when he shall begin to sound, the mystery of God should be finished, as he hath declared to his servants the prophets.

The Mystery of God is
  1. 'Christ in you, the hope of glory' - Col. 1:27
  2. The completion of the Revealment of God's Plan of the Ages.
Since the saints ('His servants') are this 'mystery,' it seems unlikely that they would also be called 'his servants the prophets,' at least, not in the same context.
(Rev 11:18) And the nations were angry, and thy wrath is come, and the time of the dead, that they should be judged, and that thou shouldest give reward unto thy servants the prophets, and to the saints, and them that fear thy name, small and great; and shouldest destroy them which destroy the earth.

In this verse the phrase "give reward unto thy servants the prophets, and to the saints" re-affirms the earlier conclusion from Rev. 22:6 that these are two distinct and separate groups.
So then, who are 'His servants the Prophets?'

Our conclusion is that this group is exactly what it sounds like. These are the prophets that came before the opening up of the new and living way. These are the ones of whom Amos 3:7 speaks of: "Surely the Lord GOD will do nothing, but he revealeth his secret unto his servants the prophets." Surely these faithful ones of old would have been part of the church class had they lived during the Gospel Age, thus the appropriateness of calling them 'His Servants' and 'Thy Servants.'
Conclusion

Based primarily on Rev. 1:1; Rev. 7:3; 11:18 and 22:6 we conclude that 'His Servants' refers to the Little Flock.

It does not appear to include to the Great Company, especially when we see the Lord making a clear distinction between the Little Flock and the Great Company in Rev. 7. In that chapter it is only the 144,000 who receive the seal in the forehead. This group is there referred to as 'the servants of our God.' When it mentions the Great Company in the last half of the chapter they are neither sealed in the forehead nor are they referred to in any way as being 'his servants.'

Since we also have 'His servants the prophets' is seems clear that God has had (and will continue to have) 'servants' (not slaves but willing servants desirous of doing His will) during every age from amongst His intelligent creation.