The manager and a different plumber came out this afternoon. The second plumber confirmed that cutting the connections to the regulator was the easy/lazy way out. The manager apologized profusely for the first plumber - the duct work is B-vent (meets code) and there is heat shielding on both sides of the wall. In a nutshell, about 80% of what the the first plumber said was incorrect.

Thanks to everyone for their help.