If the service is exposed publicly to the web, It can be crawled regardless of whatever guards are in place by the service provider. Browser emulation will be a good start.
Permitting certain search engines to crawl but not others is anticompetitive and violates the principle of an open web.
> any new search engine will have its roots in "shady" tactics of crawling.
Who cares? If you are successful enough, then you'll negotiate with them later. Don't worry about it now.
Crawl away!
It seems you can contact Yelp and tell them how you plan to use their data and maybe they'll let you crawl their site.
I really want to explore any and all alternative options before I decide to crawl away :)
if they come knocking on your door to take down the content, then worry about it.