Thousands (probably tenthousands) of JAR licenses have been issued
based on flighttraining done on N-reg.
AFAIK, there are special rules for this under JAR-allowing flight schools in foreign (non-JAA) countries to instruct on non-JAA helicopters; and the JAA CAA would accept these hours.
At least the German CAA (LBA) does NOT accept ANY flight hours flown on a non-JAA registered helicopter (other than the above mentioned flight school hours)...