Actually, there are a couple quests which involve that vault, just that none of them are acquired in it.
But it does seem like the concept wasn't really used to its full potential. It's pretty much just another generic hotel that happens to use the vault tileset, but it could have been done better. If nothing else, they could have let you actually gamble in it, I mean, it's true that it got turned into a hotel after Mr. House took it over, but I'd think that letting people gamble in it would attract a lot of customers, especially since that's what most people who go to the Strip are there for.