They can't be sold on the exchange, I tried that. Anyway... it would be nice to have the option to reclaim them if you dismiss them. I claimed mine before realizing that it could only wear KDF uniforms (I'm FED). I guess I'm OCD, because now I have someone who isn't in uniform on my bridge permanently, and it's kind of annoying.
Ideally, I'd rather just be able to give them a FED uniform, but being able to dismiss them without losing them permanently would be nice too -- it's a long way to Diplomacy T4, after all. I'd even be willing to pay a dilithium cost to get it back after dismissal.