I wash my plastic hides on a weekly basis...so if you washed all of the "shirts" that often I don't think it would be much of a problem. My old roommates used a shirt for their ball python and somehow it moved the shirt all over the cage, where it wanted to hide. They didn't wash the shirt anywhere near enough, but the snake seemed to choose that over the other hides that were in there.

Not my style or preference, but to each their own. I don't know how I'd feel about putting a shirt with urates and snake doo-doo in my washing machine.......