I signed up for Party Poker from here in Japan with no problems, using my Japanese address and contact details. I can connect fine, and I know a couple others here who are on Party with no reported problems.

Full Tilt and PokerStars also work fine for me.

I don't know about the Neteller situation - I have an account I opened here with no problem, but I haven't registered a local bank account with it. Probably best to go with what they recommend.

I don't think you'll have any real problems continuing to play online from Japan.