Capt.,
In order to use your boat commercially (for hire) in the Dominican Republic, it MUST carry the Dominican flag. This means that first, the import tax and duties on the boat must be paid. After the tax is paid, then you pay a HEFTY fee to the Marina de Guerre for the actual DR registration, the cheapest I found was over $30,000rd. This varied depending on who you talked to and how much of a cut they got. And if you get through all this, then you may very well have to pay a regular user's "fee" to your local Commandante.
I brought my 40' Sportsfisherman to the DR to charter fish the boat. After fighting for 10 months with the Aduana both here in Samana and in Santo Domingo regarding the boat's real value and subsequent tax (supposedly 42%, but they started my boat evaluation much higher)and having the boat illegally impounded during the process and kept where it sustained several thousand dollars damage (the fuel dock in Samana) from other boats hitting it, being denied the ability to move the boat to its regular anchorage in Las Galeras despite having paid for the permit to do so (I refused to pay a $3,000rd monthly bribe to Samana's Port Commandante for HIS permission), finally getting permission to move the boat to the boatyard/mooring at Carenero (owned by the then-governor and his family) where it was taken out of the water WITHOUT MY PERMISSION OR KNOWLEDGE and the keel driven through the bottom of the boat in what I and others believe was a deliberate attempt to keep me from competing with the only other sportfishing boat in the area (owned by the governor and his family), having to rehaul the boat out of the water at another yard for 78 days and costing $8,000 USD to repair the damage, I just gave up. And to top it all off, I had to sell the boat afterwards at a loss just to repay the money I borrowed to repair the boat.
Also bear in mind that what happened was not unique as I've talked to a number of people who have had a lot of problems with foreign registered boats in the DR.
Think twice before you give up your home country registration/flag and all the advantages it affords before you enter into this RISKY venture. I guarantee it's going to cost you dearly.