My "Diesel-C" has the generator on the passenger side, and behind the rear axle. The exhaust crosses over, and exits under the left rear corner of the RV...
The main exhaust system exits out the right rear, and it sure would have seemed like an easy thing, for them to plumb the generator right into it...
EDIT: the post above mine was entered while I was still typing... It seems that the mystery has been solved!