When a Sim appears in your game from another person's game, it defaults to the standard work uniform. Since this cannot be altered at all (not even the makeup or hairstyle), there's no custom content to transfer.
They do show up with things like glasses and earrings though, don't they? I don't know if all accessories transfer but I'm assuming the glasses worn by my visiting acrobat aren't part of the normal male uniform as he's the only one I've seen. So theoretically it would be possible to have custom content transfer for those things unless it's checked for. I haven't tested it, I just made sure all my performing sims are free of anything like that.
