I'm not sure the exact difference in the US WRX manifold and the JDM STi except that its long runner one piece no tgv (I got lucky and the tech didn't notice the no tgv's and passed me after comparing pics of an 04 sti manifold and a 02 WRX manifold side by side with my manifold version 8 looks like the 02 wrx since its drive by cable). If you are really paranoid about it, swap the intake manifold to the US WRX. This assumes that you are trying to get the BAR sticker for it.
If its a ej207 in a 02-05 wrx and its a normal smog shop they are not gonna notice the manifold differences. Just drop in the US wrx ecu, stock dp and smog it.