Actually the T&Cs state "Marriott Vacation Club International ownership stays do not count toward Elite membership." And I could easily see them saying that use of an "exchanged" week is really nothing more than your use of your ownership week. So I would guess that any stay where one did not directly pay Marriott for those nights as a "rental" stay, Marriott shouldn't be giving you night credits.

Of course as has been stated here numerous times, YMMV. But I think the norm is supposed to be no night credit when using your ownership weeks or stays generated through the exchanging of an ownership week.