There will be more and more of these games as companies who don't wish to get effectively blacklisted from publishing and marketing in the US once real money gambling apps become legal position themselves for market share of the faux betting space so then can switch it up when/if the legalities are changed.
Whether or not the gambling bit is legal would depend on where the company is based, but then again it's Zynga's love child, you wouldn't expect everything to be above board would you?
And it's possible this is not infringement. But it could still land them with C&D letters or answering a court filing.
The legality of gambling is dependent where their users are located. If it's illegal to gamble in Virginia, then users of the site in Virginia get into trouble for gambling or Virginia tries to get the site closed down (or maybe blocked by ISPs in VA.) But since they're using fake currency and not paying out in real USD, they'll probably be just fine.
http://www.ipo.gov.uk/types/copy/c-applies/c-applies-faq/c-a...