All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
There is no doubt that what those Hindus are doing is Shirk and clear-cut disbelief, therefore, working with them in that pilgrimage trip in the manner which you mentioned is helping them in their falsehood and disbelief and Allaah forbade this as He Says (what means): {And cooperate in righteousness and piety, but do not cooperate in sin and aggression. And fear Allaah; indeed, Allaah is severe in penalty.} [Quran 5:2]
If the work is forbidden, then the pay for such work is also forbidden.
Allaah Knows best.