Most companies are different... I know Deluxe used to have a minimum they payed pros each month, but if the royalties from a pros board sales are higher than the minimum, they get their full royalties. So if one month a pro only sell 10 boards he still gets a decent check. I've also heard of companies only paying salaries with no royalties (sounds sketchy) and I've heard of companies that only pay royalties, so if you only sell 10 boards you might get a check for $20. I believe $2 in royalties is pretty much the industry standard for pro model decks.
It used to be that ams didn't get paid, things have changed. Most ams are getting at least a few hundred a month from board sponsors and potentially a lot more from clothing / shoe sponsors. People are starting to learn the ams are where the future is, they want to keep the young guys psyched so when they turn pro they don't leave for a better / higher paying company.