No, it is not an ethnicity either. It’s like saying that being European is an ethnicity. The descendents of Italians and Germans in Argentina and Uruguay have nothing in common with the half-Indian half Spanish people of Mexico, who in turn have no tie to the Negroes of Cuba and Puerto Rico.
Per the OMB guidelines located here, hispanic is considered an ethnicity:
http://www.whitehouse.gov/omb/fedreg_directive_15