Jon Carder, CEO of Mojopages, just asked Matthew Berk if they have ever run into any problems crawling other review sites.
Matt: we are respectful of who we crawl – we typically contact the publisher first and often have partnerships.
My POV is Google does it so why shouldn’t you?
Another question re what about negative reviews? Neither Openlist nor NWSource deletes negative reviews as they are often good viral content. They encourage unhappy businesses to get their customers to post good reviews.