I'd never heard of the Panthers being supported by the USSR, but a good general rule of thumb is that anything the Americans were doing during the Cold War, the Soviets were doing too, and vice versa.
Someone here says there was an attempt by the KGB (not a very successful one, by the sound of it) to co-opt the Panthers leadership:
https://www.google.com/url?sa=t&sou...Qjjh6BAgOEAE&usg=AOvVaw0EgtHe2IsuMv6O-mg-xHRZ
It's important to bear in mind that this is a lot different from the idea that the BP were
set up by the KGB. So any Soviet activity that was intended to support them just to make trouble for the American government doesn't deligitmise them any more than American support for the Mujahideen in Afghanistan during the Soviet occupation deligitimises them as an anti-imperialist movement.