I think that yes, they used Canon(DSLRs) before, and maybe Nikon (DSLRs) before that.....I would guess that there are special contracts signed with these companies so that when there is a big sporting event (especially something like the Super Bowl, the Olympics, the World Series, etc., etc.) the AP has access to all the gear their people need during the whole time and they shoot exclusively with that gear, etc., etc. Otherwise, what would be the benefit to either the AP or the company whose products are suddenly chosen and anointed by the AP (and often other agencies as well)?
Yes, I've seen photos of gear set out on rows and rows of shelves, ready for the grabbing and use by people who are shooting sporting events or some other big news thing -- they have carte blanche and can say "I need....[name the body, name the lens(es)] and they're handed to them. This has to be all prearranged through contracts and such.
And, yes, indeed, the anointed company then has the benefits derived from having the cut lines, captions on photos, etc., mentioning the brand name, body and lens used, etc., in the usual EXIF info.