From the brochure/website
https://dynamaxcorp.com/class-c-motorhomes/isata-3
"Trailer Hitch (5,000 Tow lbs.) with 7-Way Round Tow Connection"
From the web on 5000 lbs hitchs
"Class III hitches can handle up to 5,000 lbs. GTW and 500 lbs. tongue weight. This type of hitch generally has a 2-inch rectangular receiver and is considered the "standard" type of hitch for general towing."
I'm not sure what you mean by frame mounted...I don't know of another way. But, we do not mount to the Mercedes frame, we extend that frame slightly so it is mounted to the frame that we extend from the frame.
Having said that...just because it is a 5,000 lbs hitch does not mean you can tow 5,000 lbs. There is a very long thread on that, but the shortest, easiest answer is that you can tow GCWR mins GVWR. Which is 15,250 minus 11,030 = 4220 lbs