It's not the only link which states this lol. It's even in 'The Encyclopedia Of International Organized Crime' by Carlo DeVito.
But it really sounds like BS. Maybe there was once a Latvian guy involved with the Latin Kings, eventhough there aren't many Latvians in the US. The only Latvian-American I know of is DJ Lethal.
But like you said, Latin Kings is primarily Mexican with probably still a lot of Puerto Rican members and probably some Ecuadorians and Portuguese. But Latvians, Caribbeans, Spaniards, Italians,...involved with the Latin Kings ? Maybe one or two in the history of the gang ROFL