Oops, I didn't noticed this before
(If the mod would be up to date)
the Crimson Kitchen generates upon world generation if the mod is enabled when it's generated (regardless which world evil the world has).
It's a pretty small building (at least at the moment) that generates somewhere in the cavern layer. The Crimson Kitchen Pamphlet (sold by the Waiter) should point at its direction, so it's easier to find it.

If the world was generated without the mod, the Crimson Kitchen won't be there. It is possible to craft the Crimson Kitchen Bar in hardmode (it needs ichor), and that will allows the CK Barkeep to spawn.

As a furniture-spawned town NPC, he spawns wherever his furniture is, he can't be relocated via housing flags, I think, but his furniture can be moved elsewhere - the CK bar should need higher tier pickaxe to mine up though.
Same goes for Flann, and the Cyber Fangirl (but their furniture can be moved with any pickaxe)