If you have matched the ecu to the engine, turbo, fuelling etc then the answer is probably no.
Ideally any jap import should have a remap even it has the standard ecu fitted as it will be setup to run on their 100 ron fuel and not the rubbish we get over here. That said I ran my import without a remap for over a year (with octane booster added to the fuel) and never had any problems.
If you have any doubt you could book a rolling road session, which should work out much cheaper than a remap, and they could advise you if the car was running/fuelling ok. The only downside is if it is not you may have to end up paying out for a new ecu as well.