Common sense would seem to call an ethnic group those with most of their ancestors originally in a country where a certain language was spoken-in this case, Spain and the Spanish language-and they dispersed and interbred from there.
Most people think of Hispanic as being those of Spanish ancestry in the New World-the Spanish part is what makes it an ethnic group. If you want, you can split them into sub-groups by location-but why? The Spanish we speak here is a different dialect from what is spoken in Mexico City-but so is the dialect spoken in Michoacán or Brazil-but it is still Spanish-the language originally by that ethnic group in Spain.
All three races are involved-I am to all appearances Caucasian, like most Hispanics in the Americas-but in the Caribbean and some parts of central and south America, some Hispanics are Black, and in the Philipines, they are Asian-the Spaniards spread their genes far and wide outside of Europe.