If search results that hit Yelp data linked to Yelp there'd be no problem. However if it links to Google Places because Google scraped the Yelp data and loaded it into the Places database - that's a problem.
Suppose someone launched an 'Encyclopedia Search' service that searched Wikipedia, Encyclopedia Britanica, etc and linked to their sites. The the service then started loading the Wikipedia and Britanica content into it's own respository and linked searches to that. It's still searching the same data, and taking you to the same articles, it's just that now you're not going to Wikipedia or Britanica anymore. Would that be ok? If not, what's the difference?