I only went to Siem Reap and stayed at the gay resort called Men's Resort. It was a fun place. it turns into a gay bathhouse in the evening, and locals are allowed inside for $5. The Men's Resort allows visitors as long as they check in at the front desk. I heard from friends that the rest of cambodia is the same way with as far as allowing guests inside without any problem as long as they check in their ID at the front desk. I had lots of fun in Hong Kong and Taiwan and Bangkok as well. No problem there with visitors. I love Asia so much.
Sounds like a lot of fun. I have to SR before, but what you described might is worth a new visit. lol
I would recommend to write a small report after your trip to Vietnam with info about your hotel. It might be helpful to other travelers. I'm honestly surprised that even websites specialized in gay travels don't mention how strict the guest policy can be in Vietnam. It was a bit of a shock for mew the first time in there.
You mentioned Taiwan and HK. I guess those have been previous travels cause as far as I know those two places are still closed to tourists.