In theory, I'm sure that CAT5 might work but the problem would be if there's a fire. I'm pretty sure it's not fire rated and probably not to code. If insurance gets involved, it's possible they can deny a claim because of a code violation.
This is why I disconnected some of the lighting in my house when I purchased it 2007, after finding ceiling lights wired with 12 ga speaker wire. Granted it was for standard AC lights that are usually Romex, not the low voltage for your case. But I didn't want to risk it.
