I don't know if they'd lose, but I don't know if they'd make a dent in TripAdvisor as opposed to the smaller competitors. People go where the data is, and Trip has the reviews and has the reputation for trustworthiness. Yelp doesn't have a good rep as far as trustworthiness goes--the allegations of paying to hide bad reviews, etc.--and would be starting from zero or near-zero.

(And, having seen a few organizations handle fraud in user-generated content, I think Trip does a pretty good--not great, not perfect, but better than anybody else I've seen--job of it.)