Freebore, I have been doing some digging/poking around at my local friendly Dodge dealer and I think I found the source of this confusion. When a tech sets up a truck to do a mobile regen there is a screen that pops up, it has some warnings and one of them says to have cruise control off. So, I think that dealers have inferred incorrectly from this screen that cruise control disables regen.
Thanks for the update - it sounds like a good explanation, but as you say they assume wrong.