I would think the answer is no, even if you go through immigration. I also do no think SQ's lounge at NRT is worth the effort. NH has five or six lounges at T2. Ask for a Signet lounge, if you can. It should be marginally better than the other category. If you are equipped with a wireless LAN-enabled PC, stay outside the lounges! There's now a Yahoo! Net cafe near one of NH's lounges.
I really hope NH will invest more for lounges.