I think that statement applies to Central Americans more. Tejano (Mexican) Democrats tend to line up with the 'Rats 70% of the time, despite the fact that northern Mexicans (Nortenos) have values more proximate to conservative GOP'ers. PRI-influenced Mexicans tend to vote down-the-line with whoever their neighborhood or district Party jefe says to vote for.
Dubya was encouraged a few years ago by the 40% split he got in Texas from the Nortenos and Central Americans, but I think he is overoptimistic about being able to drive much further into that overhead resistance.
The southern Mexicans who abound in California are even more hidebound, from what California FReepers have told me.
Cubans and Puerto Ricans and South Americans are another story.