I would think though that crime rate would affect more than just vacancy rates. Say you're renting in an area with a high burglary rate. The property's windows get smashed once or twice a year (and that was the only thing that went wrong for you with this robbery). I would suspect that you're going to get a call from the tenant related to this, so more work for you. And you're going to have to pay to replace the windows, which affects the property's expenses.
Or is that somehow already built into the classification system? I thought A,B,C,D had to do with property appreciation (which I could see correlates to things like crime rate), but was not a direct measurement of other factors.