Were those Death Troopers in Rebels...

vessaharja

...Zero Hour: Part 1? The ones holding Kallus.

Mullato

I believe so. Sure looked like it.

vessaharja

^ that's kinda cool. Means they aren't exclusive to Krennic (if they ever were supposed to be in the first place...).

DatBoi

They were. We'll definitely see more in season 4