Honestly, I've called cops on cops before, no need for them to be black. One because they were an undercover cop who did not identify themselves adequately and acted suspiciously, second another (or maybe the same) undercover cop that was driving recklessly through the streets almost causing accidents without even a cop light/siren. I'd probably even call if they were in uniform and acted suspiciously enough so dispatch could double check. Cops are workers and they are human, they are not above you or illicit activities themselves, recordings have proved this. I would call, just not place the blame on them while just sticking to why the circumstances aroused concern.

And even generally, calling official numbers to confirm a situation is even something that is increasingly becoming necessary with the number of scams coming out. I realize racism was probably a factor here, specially if they are calling while cop cars are outside and there is clearly a crime scene being investigated, but seriously, don't think this means you have to think twice about reporting suspicious activity if they are cops.