I'm qualified in full body massage and we do do abdomen on guys, in fact the whole massage is the exactly the same. If anything i've noticed it's the guy who seems to get paranoid/uncomfortable when getting the abdomen done.
The whole body is covered in towels, but the area being worked on is uncovered. I found it a bit annoying, and sometimes restrictive to have so many towels.
Went abroad earlier in the year and had a massage and it was the opposite of here! No towel cover, and the male masseuse tried to give me his phone number during the massage. Oh my god. They don't have any inhibitions there.