As Ron said, you can do it legally. Ron also correctly pointed out some problems. I'll point out more:
Your student pilot buddy may not be able to get insured on an RV-X because it's amateur built and because, as a student pilot, he's got low hours, and minimal experience. When I was looking at some Lancairs, I was talking to a guy who had about the same experience as me at the time (~120 hours, no IR), and he said that the requirements to get insurance in the plane were 100 hours of dual with an instructor who had 100 hours himself going into the training. Granted, I think Lancairs have a worse reputation than RVs, but the point is similar. My instructor, with 5000+ hours in everything GA from 172s to Comanches to Navajos to King Airs to... you get the idea, can only get liability on his Acrosport.
My suggestion to your friend (as someone who wanted to do something not so different as a student pilot) is that your friend finish up his PP in a standard trainer, and perhaps at that point think about getting the RV, and go through IR training in that, among other things. My goal since I started flying was to get a twin. Once I started looking into the practicalities of it (namely insurance), I decided I was better off getting some more training in more standard aircraft first. Now, at 190 hours TT and an IR, is it beginning to become a little more feasible... but I still need more training.
That said, part of my decision was based on the fact that I have such nice and inexpensive aircraft available to me for use. If I didn't, I would probably have pushed to get my twin sooner. I would still suggest your friend go through private and getting his check ride in a standard trainer, even if he purchases the RV before he gets his PPL. Really, the amount of time he's likely to take in searching for and buying the plane (figuring good pre-buy inspections and doing his due diligence on research to make sure the plane he's buying is in good condition) is probably going to take him past his PPL anyway.
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