There are plenty of those hummers around in the country, with parts being somewhat available if we are talking about the regular stuff.
Body parts are not common and most likely will be special order for your model in most cases.
Repairs are not a problem in the DR for the vehicle, unless again we are talking some major issue that requires fabrication.
The biggest issue with these models are related to theft. Removable parts are often targeted and it's a pain in the neck to keep up the evil hands away all times.
Instead of giving you advice, I'm going to ask you a question: Why? What do you expect to be the gain in this endeavor? With the price of gasoline and diesel here, it's a risky venture at least.
Forgot to add. Even though old Hummer parts may be hard to find, one alternative is to check the roadside ditches during long trips. You should be able to find a few parts here and there. They were designed for military purposes because only the military can afford to keep fuel in them and maintain them.