Marriott has an excellent FAQ about account linking, status match, points transfer, earning/redeeming points, and related subjects:
http://members.marriott.com/faq/
The FAQ uses the names
Rewards and
SPG to refer to the two programs. That makes sense because Rewards comes in two versions — Marriott Rewards and The Ritz-Carlton Rewards — which are really the same program, but branded in two ways.
Here's that the FAQ has about points earned through the two timeshare companies:
Can I transfer points I earned through an interest in Vistana™ Signature Experiences or Marriott Vacation Club®?
Points earned through an interest in Vistana Signature Experiences or Marriott Vacation Club may not be transferred between SPG and Rewards.
I have theory why Marriott needed to impose this restriction.
Marriott Vacation Club (MVC) and Vistana Signature Experiences (VSE) are two entirely separate companies, although both license brands from Marriott International. MVC licenses Marriott and Ritz-Carlton for vacation ownership. VSE licenses Sheraton and Westin (which are now owned by Marriott International) for timeshares.
MVC and VSE both have long-term contracts to use Interval International (II) as their exclusive, official exchange company for cross-company exchanges, with II integrated into both programs.
Interval Leisure Group owns II and VSE, but that's not a factor here.
Many MVC owners have the option to receive Rewards points through their ownership interest — by turning in an ownership week or Destination Points. My understanding is that many VSE owners have a similar option to receive SPG Starpoints.
It is now possible to transfer points between Rewards accounts and SPG accounts. That's a wonderful option, given that the newly combined Marriott International has around 5,700 hotels.
However, if points received through timeshare interests could be used to book stays at other timeshares, Marriott International would effectively be a timeshare exchange company. The "clean" way to prevent this is by imposing the restriction in the FAQ — even though this also prevents other point redemptions (such as not being able to use MVC ownership to stay at a W Hotel).
There have been interesting questions raised in this thread about "buckets" of points. My guess — and this is only a guess — is that points from timeshare ownership are automatically used first toward hotel stays. So the transfer restriction would only come into play if fewer points in the balance were earned from other sources (hotel stays, credit card, bonuses) than what someone is trying to transfer. That would be the straightforward way.