Welocme to the forum.
That's interesting what
Daveinet had to say or what the dealer he talked to said. I have no idea as to the validity of that assertion as I personally haven't heard that before.
However, I have observed quite a few MINIs on tow dollies through the years. I have no idea of the year or the model but I have seen them on the road and at rest stops, RV parks, etc.
I did a online search and found quite a few pictures of MINIs on dollies but again, I have no idea of the year or model. Below are just a few:
HERE
HERE
HERE
HERE
HERE
I'm thinking you already know this but if your MINI has a manual transmission with a clutch pedal (not a DSG) and it's front-wheel-drive, there is a possibility that you can flat-tow it depending on the model (there was a recent thread where a member here was having a difficult time finding baseplates for one with a sports suspension but certain model years with sport suspensions have no problem with fitment issues).
MINI does not and as far as I know, has never approved any type of towing behind a motorhome. Therefore, I'm thinking the reason for what your dealer told you. However, many flat tow MINIs with manual transmissions and front-wheel-drive as well as use dollies with the front wheels off the ground.
I believe there are threads here on this forum that featured members towing MINIs on dollies. I'll do a search and post again if I find them.
Here's also a video of a tutorial where somebody is loading a MINI on a dolly:
The search of the forum I did came up with threads about dolly towing older MINIs but didn't appear to be one as new as you have:
go HERE for the search results