I lived in Weehawken for a couple years one block away from Union City before buying a condo in UC off of Park Ave. by the Pathmark across the street from Weehawken, north of Rt 495. My wife and I are Asian with no kids right now.
Yup the majority of the population is hispanic...87% is a good number. If you're going to get anything in UC, I recommend north of 495 and furthest east you can get, closer to Park Ave. and Blvd E. I'd stay away from downtown UC or the area south of 30th St as things go a bit downhill from there and most crime in UC happens down there where you get closer to the JC borderline. For the most part UC is actually fairly clean compared to many other poor communities where garbage is rampant. Most buildings and houses are dated with the exception of new condo/apartment buildings that are around.
It used to be mainly Cuban which its not so much anymore but there are still clusters of them around. Unfortunately its a ripe environment for illegals to come into. Doesn't help the school system when there's so many people not paying taxes in addition to many living at or below the poverty line.
Anyhow my wife and I chose to buy a place here because it'll be 7-8 yrs before we even have kids so at least 12 yrs or so before they hit school. We bought our condo which was a short sale and the place was only 4 yrs old. The bus line runs right to the PA and the Hoboken PATH Station where we are. We believe this area where we are in UC is prime for up and coming. But because of the recession and everything, development and people buying and moving here took a dip and it has regressed a bit. The taxes are less than half of what we would pay in Weehawken and Hoboken for a similar sized 2BR, 2BA condo. So until we have kids, this is a good spot for us
Overall it depends on your situation though
Hope this helps from a UC resident