If my recipe calls for white rum and I only have Jamaican rum can I still use the same measurements? 
It really depends on the recipe. Dark rum tends to have a more complex flavor, heavy on molasses. As long as you like that and feel it will go well with the rest of the recipe, it is fine. It isn't going to make any substantial chemical difference in a way that will affect the outcome, so base your decision completely on flavor and color. 