I've tried to use the "particle" command to spawn some particles to a WitherSkull entity, but it didn't work, I tried as well to spawn them to a SmallFireball entity, with the same result.
I found this bug also in other commands, but I'm not sure about them.

Command used:
/particle wake ~ ~2 ~ 0.2 0.45 0.2 0 40 @e[type=WitherSkull]