JR,
I belonged to MAAC a few years ago and belonged to two AMA clubs and had no problems doing so. I'm not an insurance lawyer, but the president of one of the clubs was Canadian and he didn't have any problems with it. Why I brought it up was that so many people don't want to join AMA and if they join UMA, they would run into the problems you listed. From what I gather on related forums, perhaps some people just want insurance and MAAC might be an alternative other than UMA.
As far as I know, there are no legal problems belonging to MAAC and flying in the US permanately. My philosophy is, for every problem there is a solution, it seems it's just the opposite for too many others.
Take care,
CCR
http://www.kites.org/rc_instructors