I am a Wyndham owner, active on TUG, and I'm 99% sure this is not correct.
Wyndham has done a lot of things to attempt to curb renting. But as far as I know, this is not a rule in the system. It is certainly not present in the Member Directory (which does articulate many the other rules, including the overlapping-reservation rule and the Owner Priority restriction.)
There is a chance that I'm wrong about this, but I don't think it is a very big one.
The thing that Wyndham
has done is that it has used its discretion in specific individual cases to decide that an owner has violated the commercial use clause without precisely defining how that clause is interpreted. They've used their position as first-mover to preemptively make that declaration, and put further restrictions on individual owners' use of guest certificates. I suspect it is possible (and maybe even likely) that an owner in this situation could prevail in court. But Wyndham will make that very expensive and time consuming along the way in a war of attrition.
There is no reason, in principle, why
DVC could not do the same thing with specific, individual owners. I know that if I had a side business of renting DVC points, I'd have a ready exit plan. The buy-strip-flip folks are well-positioned here, because their model already incorporates a short holding period and a plan to sell quickly.