They claim to be operating out of the US, and the address listed is a half empty strip mall in the Las Vegas suburbs. They post no licensing details. Seems legit?
They managed to get a BitLicense (one of very few orgs to do so) which at least somewhat lends to legitimacy. Also pretty easy to find the people involved, and a founding team of infosec people is a pretty decent means to start an exchange. https://bittrex.com/home/about
As far as I can tell they do not have a BitLicense, they just applied for one. The wikipedia page you linked even includes the 3 companies who have been granted one so far, and none are Bittrex.
