So maybe some racist white people might rate any area with black or Hispanic people as unsafe. Hopefully, if the area is actually not bad, some non-racist black or Hispanic people will rate it as such. The positive and negative ratings should cancel each other out in such cases.
The areas that end up with negative ratings would have to be rated such by users of all ethnicities, which more or less rules out too strong a correlation with race here.
The only problem is if somehow only a single ethnic group, like white people, uses this.
So, basically, I don't think this is going to be an accurate source of information here. At the same time, if it were to actually get widespread usage, I don't think it would be as bad as some people are making it out to be.
Ultimately, though, why not use something like city-data? The site is ugly as sin but it has basically all the information you could ever want.