First, if by triad God you mean that trinitarians believe in 3 gods, well, that's just not true. They don't believe in that. ANYONE, like the JWs, who teaches that the doctrine of the Trinity teaches that God Almighty is 3 gods is wrong. Worse than wrong, but a liar. And we know who is the father of the lie.
Christian Trinitarians are monotheistic and do not worship three Gods as the Jehovah’s Witnesses claim.
The Jehovah's Witnesses continue to imply that Trinitarian Christians worship three Gods, not one; that they are tritheistic, not monotheistic. The Jehovah's Witnesses draw parallels between the Trinity doctrine and triadic pagan worship which they claim is the ultimate source of the Christian Trinity, influenced by Babylonian gods who were worshipped in threes, the Egyptian three-fold gods of Osiris, Isis and Horus, Italian triune godheads, the Trinitarian Hindu group of Brahama, Sira and Visnu, and on and on (Should You Believe, Chapter 5).
But this is false and unfair. The Christian faith is completely monotheistic, and worship is directed to the only one true God Almighty who happens to have a threefold nature: “We do not confess three Gods, but one God in three persons, the “consubstantial Trinity,” (Catholic Catechism, 75). “[T]he Godhead of the Father, Son, and Holy Spirit is one, their glory equal, their majesty coeternal.” Athanasian Creed; DS 75; ND16)” (ibid., 79).
Tritheism, the worship of three Gods at the expense of the unity of God is yet another pitfall which the Trinity doctrine specifically seeks to avoid (Oxford, 1211). And simply because the Jehovah's Witnesses are unable to grasp the meaning of “hypostases” or “Persons” does not entitle them to ascribe to Christians beliefs they do not hold.
Secondly, I'm not sure what you mean by Jesus being "part of" a triad god. The triune God is one, and before creation existed in three hypostases, the Father, Son and Holy Spirit (immanent Trinity). Jesus is God-man, the hypostatic union, the Word (Second Person of the Trinity) incarnate, a divine person who assumed a human nature. The humanity of Christ, the creature, Jesus, is not God the Almighty. This is orthodox Christianity. If you believe that Christendom teaches that Jesus the human creature is God, then that is completely wrong also, another lie perpetuated by the Society.
In most formularies the doctrine is stated by saying that God is one in His essential being, but that in this being there are three Persons, yet so as not to form separate and distinct individuals. They are three modes or forms in which the divine essence exists. ‘Person’ is, however, an imperfect expression of the truth in as much as the term denotes to us a separate rational and moral individual. But in the being of God there are not three individuals, but only three personal self-distinctions within the one divine essence. (New Bible Dictionary, 1299, 1300)
“The humanity of Christ is a creature, it is not God” (Catholic Encyclopeda, 922). Jesus is a divine person who assumed a human nature. If you're truely interested you can get more information here: http://144000.110mb.com/trinity/index.html
Is there any evidence in the Old Testament for a triad God? What about other Jewish texts?
The evidence is meager, but Trinitarian patterns are evident in the OT. Read more here: http://144000.110mb.com/trinity/index-4.html#18