if FAA/US only pilot flew as safety pilot (and not as instructor) that legal with some caveats done to death on pprune and gazillion other websites. The European/non-US pilot would be the only PIC in their books, but as per FAA regs, when the handling/controls manipulating EASA etc chap is under hood, then the safety pilot is acting as PIC keeping lookout etc. I don't see why European guys could not have it OK'd by home CAA when the other person is not instructor/instructing. Logging lots of time as S/P in FAA system may be frowned upon by some companies, though.