The NFL wants nothing to do with Las Vegas, for obvious reasons.
Yeah, that market would be a bigger disaster than Jacksonville. Jax has the potential of drawing fans from Southern Georgia and Northern Florida, while Las Vegas has just Las Vegas. All right, they could draw fans from Lake Havasu City, Kingman, Bullhead City/Laughlin, Pahrump, Mesquite and Saint George as well. Never underestimate the potential from Pahrump, either.
If Vegas ever got a team, I seriously doubt that gambling would be a problem with it. They keep a tight lid on things and would make sure that the gambling stay separate from the local team, most likely forbidding gambling on them at all. And as long as the mob gets a big enough piece of the action, they would see to the strictest enforcement.