I figure there are two possibilities. Either 1) they are speaking out, but since it doesn't fit the media narrative, they aren't getting any airtime, or 2) they are putting politics above race for this one, for their own "greater leftist good".
Even the conservative media has not been reporting Hispanic support for Zimmerman, so I don’t think it is simply the media narrative quashing the story. I am afraid you are right about the second explanation: leftist and Democrat politics over race.