No, they have never believed in Jesus in the Christian sense. Their beliefs are a modern incarnation of Arianism which was a heresy condemned in the early Church.
They believe that Jesus existed before He became man as an angel, particularly the Archangel Michael. They reject the teaching of Scriptures and the Church that Jesus is one with the Father and the Holy Spirit. They deny totally the personage of the Holy Spirit.
They claim that they preach the good news but instead preach from house to house a perverted Gospel that makes Jesus' death on the cross to no effect for mankind for if Jesus was not God as He claimed, He could not have been the perfect sacrifice prophesied. Therefore, our sins have not yet been atoned for and the messiah is yet to come, not again but for the first time.
If that is not enough of a perversion of the Gospel they also teach that Jesus did not rise from the grave bodily but as a Spirit and that His body corrupted in the grave. Therefore, Christ has not risen in the Christian perspective. Then, of course there is the problem of their belief called "Annihilation" where they believe that God only rewards those who are deemed worthy with eternity while all the others simply cease to exist. This teaching denies the true justice of God described in Scriptures.
All these perverted beliefs are taught by using a proof text methodology which ignores context in favor of supporting their doctrines. Many fall for such deceptive tactics. The Bible speaks in prophetic warnings of such groups focusing on drawing the faithful from the truth:
(Mat 7:15 DRB) Beware of false prophets, who come to you in the clothing of sheep, but inwardly they are ravening wolves.
(Mat 7:16 DRB) By their fruits you shall know them. Do men gather grapes of thorns, or figs of thistles?
(Mat 7:17 DRB) Even so every good tree bringeth forth good fruit, and the evil tree bringeth forth evil fruit.
(Mat 7:18 DRB) A good tree cannot bring forth evil fruit, neither can an evil tree bring forth good fruit.
(Mat 7:19 DRB) Every tree that bringeth not forth good fruit, shall be cut down, and shall be cast into the fire.
(Mat 7:20 DRB) Wherefore by their fruits you shall know them.
(Mat 7:21 DRB) Not every one that saith to me, Lord, Lord, shall enter into the kingdom of heaven: but he that doth the will of my Father who is in heaven, he shall enter into the kingdom of heaven.
(Mat 7:22 DRB) Many will say to me in that day: Lord, Lord, have not we prophesied in thy name, and cast out devils in thy name, and done many miracles in thy name?
(Mat 7:23 DRB) And then will I profess unto them, I never knew you: depart from me, you that work iniquity.