As Gerald says, there are different systems, both made by Monaco. When we had a 2003 Holiday Rambler Endeavor, the cruise would not come on if the exhaust brake was turned on and engaged first. If it was not on, the cruise could be set, but once the exhaust brake was on and applied, the cruise would not resume. I figured out that if I pulled over, or at the next rest stop for fuel or just a break, if I shut off the exhaust brake, then the engine, the cruise control would come on and set after re-starting the engine.
The Beaver runs with both the exhaust brake on and the cruise control on at the same time, and if the exhaust brake is applied, the cruise will still resume. Or if the exhaust brake is on, and applied or not, the cruise can still be turned on and set.
Stan