well, the term hispanic refers specifically to a spanish speaker or that which derives from spain. certainly dominicans would fall under this category, but haitians would not. haitians could be categorized as latinos from the francophone line.
the use of the term hispanic to describe latin americans is being phased out for a number of reasons. the preferred term now, latino, is derived from latinoamerica, which is already a step up from the term hispanic. also, a spaniard is hispanic; it is hard to lump him in the same category with a quechua speaker from the peruvian andes. third, i think hispanic is a phonetically more anglo term than latino is, which also has come into play.