jahez is the stuff you get from your family to take with you to your new house, so it can include new clothes, jewelry, shoes, houseware stuff, furniture, you name it!
I dont know, in my family they didnt put ubtan on the bride during the mayoon. Maybe they do in some families? I think more often now, people might just have an ubtan paste, and to keep up the tradition, they might put a dot of this paste on the girl's cheek or something, but I haven't seen anyone (yet) go all out and put it all over the girl's legs and arms and everything, especially in front of the large crowd that's present!
Calling them "hindu traditions" is a bit simplistic...whats an "Islamic tradition?" I mean, most Arab weddings I have seen are just like Western weddings, the brides even wear white dresses strapless/sleeveless dresses like prom gowns with a veil. As far as I know, the mehndi ceremony is also not an Islamic tradition in the sense that its not required as a part of your wedding, its just a cultural thing. Nikkah is obviously required, and then I believe you have to have a valima (or some ceremony after the nikkah) as a sort of proof that you're married and to present yourself as the married couple. This is my limited understanding.
My point is that, in my opinion, there are few traditions that can traced back purely to Islam. Muslims have one religion but come from different cultural backgrounds and I think its important to embrace that too, rather than pretend that we all just never came from India, didn't take anything from that culture and still dont share plenty in common with them, because we did and we do!