yeah, it likely wouldn't hold. you'd really have to reinforce the bracket to multiple places on the body panel, and i bet to make it strong enough, you'd really hate the way it looks. i've seen one on a blazer and one on a bronco where they ripped out of the body... scary sh!t if you're cruising down the hwy.
the thing i don't care for about most of the swing-out style spare tire carriers that attatch to bumpers is that they typically don't conform to the forward slant of the body. however, it wouldn't be too hard to build one that did.
have you considered one of the swing-down, stinger style bumpers? that style is my preference. i'm getting ready build one soon...