I've never heard of any organization signing players solely based on race since the 60's. They simply don't care.
That said, MLB teams signing regional players is nothing new. Heck, even the Cardinals have had a ton of guys from Missouri on their team, the Astros have always liked guys from Texas, and etc.
The bottom line is, it's not about race- it's about putting people in seats. And having local guys has been proven to successfully do that. Fans like to see the "local boy done good".
Actually, I think this is a welcome change for the Marlins. Their biggest market should be the Latino community. This is about them reaching out to them. They have to do what they are doing if they want to survive- or they'll have to move somewhere else. That's why they've built a new ballpark and changed the named to Miami.
If they really want to reach out to the Latino community, they'll lower their ticket prices. I think if they had dirt cheap tickets in the entire outfield- I really think they would clean up.