This is correct and it is disturbing in its impact.
If your rich uncle wants to "sell" you his $10,000 timeshare for $2,500, it is not really a sale for $2,500; it is a sale for $10,000 + a simultaneous $7,500 gift. If this is unscrambled -- the sale is made for $10,000 (with the purchase and sale agreement so reflecting) and a $7,500 gift check is given to the niece/nephew purchasing for $10,000 -- the transaction will pass ROFR.
This is not fraud; the uncle wouldn't sell to a stranger for $2,500. The uncle is making a gift to the niece/nephew of $7,500 (perhaps made the day before the purchase and sale agreement is signed). The beneficiary of the gift is the relative, not Marriott; Marriott is not entitled to use ROFR to capture a gift.