I’ve picked my numbers from each of these countries’ censuses, whereas your source claims an estimate, and I cannot verify their methodology because source of that table takes me to an unrelated telegraph.co.uk article (likely a bug in the wikipedia article).

Either way, if the OPs hypothesis is true, we should see a change in corruption levels with minority percentages. I’m not an expert in Eastern European criminology, but I highly doubt that is the case. There might as well be Eastern European countries with substantial Roma population, for some definition of “substantial”, but that doesn’t change my original point that high cultural homogeniety and high police corruption definiely does co-occur.