wouldn't it simply be obtaining software via unofficial means rather than piracy since he already paid for it?

Indeed it would. Piracy it is not.

I haven't heard of Apple's legal team going after anyone for OS X piracy. Either you've purchased the Apple machine already, so whatever, or you're trying to make a Hackintosh in which case it's a bag of hurt anyway and probably not that lucrative to go after you. (Besides, the legal team is busy with Samsung, anyway - much more money in iPhone patents.)