I don't think WiFi had been invented last time I went there in 1992! They don't seem to mention anything on their website but why not e-mail them for the info at info at eldelfinverde.com
They have wifi at el delfin verde, we used it last year. Check which network is available( they have two networks on the site), then go to reception, tell them which network you can receive and they will give you a username and password to log in with. The rates are hourly, and quite reasonable, and the more you buy the cheaper it becomes. Remember to log off when finished or you will use all your airtime.