as a group of 6 guys you should take a private half day charter 4hrs, the boat and crew for you alone. rates are $650.- per charter boat including roundtrip transportation by the services of Punta Cana Resort & Club, english speaking tournament experienced Crew, waters, softdrinks, beers, Ice, baits, Penn Intl and Shimano trolling gear and all taxes, no further fishing licence required.
to answer the OP post about the fishing license stuff clearly, our country does not require any kind of fishing license for fishing from shore.
PRIVATE fishing with your own boat in dominican offshore waters does not require a separate fishing license neither, that's included in the Tax`you paid to get the "Permiso de Navegabilidad" for your boat when registered to the dominican Port.
for comercial (sportfishing with Tourists/Visitor aso) offshore fishing a permission is needed, but there still does not exist a separate 'fishing' permission, so it is included in the 'watersports activities' permission, what means that each outfitter/company/fishing seller who want's to bring you offshore for deep sea fishing needs a watersports license, otherwise the offered activity would not be sold legal and hereby not covered by any insurance.
so you as the visitor/guest/client do not have to purchase a license for any kind of fishing, sellers/outfitters like the above mentioned "Firstclassfishing" should understand that is is time to legalize their business and get their needed permissions after several years of .... luck.
to get Tarpons from the beachs in the hotel area is possible but also a very big lucky shot.
you can get lucky on Tarpon near the pier of the fuel station at the Club Nauticus and the pier of the Marinarium Excusion in Cabeza de Toro and you always find Tarpons (the smaller 25lbs class) at our piers at the Punta Cana Marina, but we would not allow anybody to target them, private Marina, our private pleasure.
have fun
Mike