That made me pause too. Here are some fanwankings I have made of it!

Firstly, I'm pretty sure that this issue was published before Nightcrawler's debut, so the belief-of-the-holder would be a retcon anyhow. Quincy Harker doesn't give the impression of being a devout man, but religious symbols work for him when fighting Dracula, so. Maybe Wolverine just did it wrong? :/

Secondly, Taj would likely have seen the crucifix work against Dracula in his travels with Rachel Van Helsing and gang; in such a delicate case as his own son I'm sure he would want to try everything he could.

Thirdly, his wife may have put it there in desperation, having been alone with the vampire child for so long (what a dick move, Taj).

Fourth, they might live in an area where Christian iconography isn't uncommon, they may know Christians.. the boy may have grown up with a mild accidental belief in Jesus.

I definitely agree there should be Hindu symbols in evidence, but I don't think it's necessary to remove Christian ones. Dracula is so into cursing God that it makes sense to me that protecting against him/his influence in this way makes sense. Particularly actual Christian stuff (proper crucifix with dead Jesus on cross), rather than a makeshift finger-cross. I'd argue that it may have been the crappiness of the crossed fingers that make Dracula laugh at Wolverine, and Kurt's extreme faith which made such a rubbish cross actually work.

I'll look out the rest of the Fashion Revenge story, then! Glad you enjoyed it.