Will my rainbow shark hunt Blood fin tetras?

yup, and you should only have one shark per tank or they might fight

No, it's a catfish, it would only be interested if they were sick or dead. You can only have one per tank and they dislike other bottom dwellers, but they don't hunt. They are omnivore scavengers and don't bother free swimming fish, even fry would have to swim past their mouth, because they wouldn't chase them.

No. It's not related to any type of shark at all. It's just a cyprinid. Related to carp and minnows.

EDIT: Although they might be a bit aggressive, they're unlikely to attack a school of tetras. I've kept them in community tanks, they're not only for species tanks.... I find Angels keep them in check pretty well. Also, Marcus, they're not cats, they're more closely related to carp/minnows.