The question may be tackled by dealing with your idea that, "If some are happy for Him to be their God and serve Him joyfully, but others are fearful of Him because of impending judgement, then at that level there are two groups." That would dispense with any need to ascertain if "and" should come between God's servants, and those who fear God.
There is another occurrence in Revelation of a group who are called to fear God, with a direct link to coming judgment. It is very helpful to sort out who this group are, for then we can see whether they are the same as those who fear God in Rev. 19:5. Here is the quote that is linked, but remember that this is symbolic language:
"And I saw another angel fly in the midst of heaven, having the
everlasting gospel to preach unto them that dwell on the earth, and to
every nation, and kindred, and tongue, and people, saying with a loud
voice, Fear God, and give glory to him; for the hour of his judgment
is come: and worship him that made heaven and earth, and the sea, and
the fountains of waters." Revelation 14:6-7 K.J.V.
Note the differences. (1) The text in question shows the command to praise God is from a voice that comes out of God's throne in heaven. The earlier command in ch. 14 comes from one angel who is not in the throne-room of heaven, but in mid-heaven. (2) The text in question shows God's judgments in destroying Babylon the Great prove God's judgments to be righteous. The earlier command shows that God's hour of judgment is on the cusp, and therefore, all men on earth should fear God and repent. (3) The text in question refers to those who believe in God and who attribute salvation, glory, honour and power to this Creator God (vs. 1). The earlier command is addressed to people on earth who are in need of so acclaiming God, the implication being that if they do not give glory and worship the Creator God, out of fear of his coming judgment, they will discover his wrath.
That is why that angelic command is 'the everlasting gospel'. It is not new. From the beginning, men have been called to worship God as Creator, out of reverential fear of his power and glory in so doing. That is why John the Baptist proclaimed the beginning of the gospel once the Messiah had arrived, for it is the gospel of Jesus Christ that the Bible consistently points to. People were called to repent, which would prepare them to receive Christ's gospel of salvation. Here is an explanatory quote:
"However, the voice and sight of angels does not - and cannot - save
them, any more than that mere beginning of the gospel which is all
that the angel preaches. Nothing less than the very voice and sight of
the Son saves through the gospel, and at that, in its fulness from
beginning to end...
Not only has everlasting no end, but by definition it had no
beginning. And if no beginning, it must take in the creation, and
speak from it... Paul begins to expound this everlasting gospel
systematically at Romans 1:18. 'For the wrath of God is revealed from
heaven against all ungodliness and unrighteousness of men, who hold
the truth in unrighteousness', [vs. 18]" The Revelation of Jesus
Christ, pp 372-374, John Metcalfe
Just as people who heard John the Baptist but who had no fear of God unto repentance failed to find salvation in Jesus Christ when he came very shortly after that call, so those people on earth in Rev. 14 who ignore the angelic call to fear God as Creator and to repent will experience God's righteous judgment.
This means that the ones in 19:5 have already acclaimed God and thus are before his throne in heaven. They are glad, and rejoice at the imminent 'marriage of the Lamb'. But those who have not repented out of fear of God as Creator will not know his love; they will only know his judgment of righteous wrath. Not so all those in ch. 19! Their reverential fear of God has led them to repentance and acceptance in the Lamb. All who are God's servants have that reverential awe of God, yet they are not fearful of any judgment to come because the love of God is their portion, even while on earth. Then, when before the throne of God in heaven, they are part of the innumerable multitude worshiping God with joy. The idea of categorizing one group as different from another is irrelevant to the context of chapter 19. All in heaven, who have been created by God, worship and praise him as one, with no fear of judgment, for that has passed and they know God's judgments to be true and righteous. Be they angels, who serve God as messengers, or humans who served God on earth but are now serving in heaven, they all serve God in reverential awe.
Sadly, those on earth who have no fear of God as Creator will not repent, and so they will be judged to damnation, for the very hour of that judgment is about to break upon them (ch. 14). But those in ch. 19 have no fear of judgment because they are now before God in heaven. There is no impending judgment for those in ch. 19. Once that is seen, then the question is answered. Whether they served on earth, or as angels in heaven, they all remain God's servants who fear him with reverential awe and joy, for eternity.
