From Rap Dictionary
East LA hispanic slang, meaning homeboy. "Vato, cholo, call us what you will" -- Kid Frost (La Raza ).
Ése or 'És' (for short) means the same thing.
/* noun */ Vato and Ese are interchangable and essentially mean "dude" or "man". These terms have been used for decades by Hispanics across the southwest. Modern gang culture has lent a more gangster feel to these terms, however, there original meanings are more relaxed and not derogatory.
A cholo is a person of mixed native American and Spanish decent. Cholo is derivative of the Peruvian word for mutt. Originally (circa 1600ad), this was a derogatory term, but generations of usage have soften it's meaning.