Arbenz not being removed probably averts the civil war as we know it. Decree 900 was incredibly popular with everyone but the ruling elite and United Fruit. Though of course, some sort of reaction is inevitable. How it goes, I'm not sure.
The problem with the notion of a successful US occupation of Santo Domingo is that roughly 40% of the male Dominican Population has military training and weaponry of some sort, however outdated and/or spotty that might be. This is all out of a 400,000 strong armed population with a large amount...