I found what I had previously read on the topic, and while several individuals verified that this is the case, I'm not satisfied as to the rationales, either.
Here's the thing, it can't be because of the posture of your property interest, or lack thereof, in DVC. This is true, because one's credit score can be impacted by any breach or delinquency on any contract, not just ones concerning real property (think of doctor's bills, which are contracts for services, primarily).
I don't know enough about credit reporting to definitively state why it's not reported, but, if it has anything to do with the UCC (which governs such contracts), it may simply be that Disney is "contracting around" standard terms dictating credit reporting. Disney can then present this as a perk to get the buyer to finance through them, while it may also afford Disney some benefit (easier process for repossessing upon default? I really don't know. Maybe there is no other reason than wanting to make a better sales pitch).
They may be able to do this when other companies would be obstructed by the FCRA or FBCA since the entire transaction (purchase & financing) are occuring within branches of the same company (just a guess--again, I know very little about credit reporting).