"Are the AMA rules generally used in scale contests?"

That TOTALLY depends on who is holding the contest. I entered one, once, and came away soooooo disgusted, I NEVER did again, at that club. It was a total joke.

"I urge you and anyone interested in competition flying ( great-fun ) to attend a scale contest, at least as a spectator and at best, someone's "caller" / co-pilot.
Doing this will answer many if not all of your questions."

Be certain that it is with the club that you intend to participate with. As I indicated above, all contests are NOT created equal, but usually precedents prevail.

Les