At least on a Rodeo, there are only two bolts holding the the front bumper on, and those are not enough (IMHO) to support serious winching. Most people drill out another hole and add another grade 8 bolt to help stabilize the front.

Since the bumer ties into the frame, I don't think you'd have any problems with a winch bumper bolting directly to the frame. Add some brackets to raise it to the same level as the body, and you're increasing the moment arm when winching. This'll put much more stress on those bolts and mounting points. It's the same when you try to free a bolt with an 8" handled ratchet, then slap an 18" breaker bar on there and it spins right off.