Well, I have no problems with the same setting in two different sites, but I prefer the premise to be different, like my two RPs here have the same setting, but different premise, or at least, the same universe, different time and different characters.
I can't see why he would do that, but... it would make a "parallel universe" in my RP... kinda hard to keep track of, and not very conducive toward story telling. But that's just my take on it.