When I had the MM pizza in Florida, the rim of the pizza was indeed sweet, but a pleasant sweetness with some complexity. However, that doesn't mean that the rest of the crust wasn't also sweet. The sweetness there might have been masked by the sauce, cheese and pepperoni. In my own experiments, I have found that I have gotten the best results from a sweetness standpoint by using the Grandma's Original molasses and light brown sugar. Right now, I am looking for the right balance between those two ingredients. For example, when I tried using 7% Grandma's Original molasses and 4% light brown sugar (Imperial brand), the crust had decent sweetness but the sweetness of the brown sugar predominated too much over the more complex sweetness that molasses imparts to the crust. I think that that is the phenomenon that Biz referred to in his post of the results of his latest Saturday night MM clone pizza. In my most recent experiment, I am using more Grandma's Original molasses (9%) and less light brown sugar (1.5%). I am less worried about the dough and crust coloration, although the dough with that combination looks to be close to a real MM dough.
The above said, there is no reason why MM can't be adding something to the rims of their pizzas, at least in some of their stores, to get a sweeter rim. The only closeup I have seen of the garlic butter that is brushed on the rims of the MM pizzas is at 0:33 in the Dustin MM video at . While it looks like the water, milk solids and maybe the garlic powder have settled out at the bottom of the container, to make what looks more like ghee (clarified butter), there is no reason why a sweetener could not be added to the garlic butter. I have not read or seen anything to support that possibility, but the possibility can't be ruled out either. A sweetener in the garlic butter could also impart a shine to the rim of the finished crust.