Sixty minutes is more than the minimum connecting times. And NRT ground and ramp services are notoriously efficient, which means that your bag has an even greater chance to make the connection than you do.

When you check in at BKK, ask ANA if they can issue you a UA boarding pass. They should be able to do so.

I'm not sure why you wouldn't book your flight all the way to BKK and back on United. Yes, ANA has superior service. Are you trying to avoid an early morning departure? Considering your name, this may be the case. The United flight does depart BKK 1.5 to 2 hours earlier, but for the stress you might endure connecting, why not just stay on UA?

I figure it this way: Even an 0830 departure means I have to be there at 0630, which means that I'm still going to lose some sleep getting there. So why be both sleepy and stressed, when I could be unstressed and merely sleepy?