Marriott may provide some guidelines that the hotels can choose to use (or not), but it is still the hotel that really decides, not Marriott.

Now Marriott probably does enforce some minimum requirements around a hotel's use of a particular rate (i.e. Gov't rate). If they are going to offer it, then listing the Federal Rate means that have to allow Federal employees on official Gov't business with the appropriate forms of ID use that rate. Of course the hotel in question could also allow non-Federal Gov't employees to use it as well (if it wanted to.)

In a similar manner, Marriott enforces CL rules. There are minimum requirements around those, but a hotel is free to add to those and provide more. So one hotel may provide more food offerings than required. Another hotel may allow more than just a Gold/Plat+1 to have entrance, etc.

So the moral of the story, is one can always call up the hotel in question and ask if they can use a specific rate. The hotel may not have to allow it, but I've seen a few be more than willing to expand the available pool of those who can use that rate. Just be willing for the hotel to say no, if you aren't in that specific pool.