yep... have experienced this first hand with our (me and my wife's) two PSP's.
We have a Japanese unit and a US unit. We also have each of us, a copy of Ape escape US version, and we can link up and play together on that. Yet, we each of us have a copy of Lumines as well, mine is Japanese and hers is US, and they will not see each other when we try to play multiplayer....