I don't think they test for racism as a side effect, so you can't say that definitely. I actually think it's very possible that certain drugs can have irrational fears and phobias/-isms as a side effects.
This is such an ignorant meme. Ambien probably does have the side effect of removing your higher level filter, and so a joke slips through that would otherwise be short circuited because of its connotation when understood in a wider cultural context. Sleep walking on Ambien impairs just that sort of higher level cognitive processing.