Yes I think you would have to be a permanent resident first. I think if your goal is to become a Dominican Citizen then it makes sense to get permanent residency. If it is just to spend time here than I see no need for it unless the rules here means you have to have it to be here more than 6 months. For business and buying property you can use your passport and I think that is recommendable anyway.
To follow up on this. I would think to work here you need residency but if you are an investor in a business or a real property it is not necessary.