Yes but ghouls would have to have something balance out the immunity to radiation.
Not really, as long as the player is made aware that it would be terribly overpowered, they have a choice. Lore consistency is a fairly big issue, and I'm almost enitrely certain this is exactly why they were left out. Thing is, it doesn't matter if they're not balanced, as long as the player is aware of it they can make a choice themselves.
Then again, it would be easy to balance really. True, ghouls have slight regeneration and rad healing, but they look like corpses, most people hate them and they're more prone to crippled limbs and the like. Considering just how important speech and other dialogue checks are in New Vegas, having people dislike you and having penatlties to skills like that would be a fairly big hindrance.