That's the written policy but (much like many of the other Marriott written policies) that is not necessarily the case in practice. I've stayed many, many times in cases where the room was direct billed to my company. In may cases, it was billed after-the-fact rather than prepaid as in the the OPs example. I've always gotten points in the direct-bill after-the-fact situation.

I'd suggest calling the hotel and giving an explanation of "When I check out, I got a copy of my incidentals folio, but not the actual room folio" and ask them to send it to you. Then use that folio to submit to Marriott for reward points. They might turn it down since you didn't pay for it, but IMHO its worth the effort.