After much reading, I have come to the conclusion, there is no written policy requiring that the operator of an SMP vehicle must be in uniform. (I'll even add this caveat, the writers of said policy likely presumed that the vehicles would be operated in the operators dress of the day, which likel would be a uniform of sorts, however this research was originally set off after I recieved a rather lengthy chewing out for being in an SMP vehicle, in civillian attire, my dress of the day as had been ordered by the RSM. My troops then recieved a similar chewing out from the same person, being as they were in a different location in the same dress.)
I checked DAOD 20-9, the DND transport manual, some other manual I don't specificly remember the name of (DND Drivers manual? Somthing like that, it was a few weeks ago), and finally, just because if anyone's got their rear end excessively clenched about somthing, it's gagetown, I even checked the BSOs for Gagetown. Nothing. There is no written regulation that I could find requiring smone to be in uniform while operating a SMP vehicle.
If anyone would like to show me otherwise, I'd be more then happy to accept being wrong, however, as I said, it's become a major pet peeve of mine, when people quote "regulations" and "policy" based on their own assumptions and ignorance.