If you’d send them only on suicide missions they wouldn’t cooperate. Still, each Nazi on the front is one non-Nazi not needed at the front.
As to heroes: Needs must. In Germany we’re nuking Nazis in the military from orbit, we’re also disallowing Nazis from fighting in Ukraine’s foreign legions, because we don’t want to have Nazis skilled in combat. That, however, is a secondary concern when you’ve got Russia invading you.
As to heroes the second: The likes of right sector are very unpopular, politically speaking, in Ukraine. There’s plenty of non-Nazi war heroes – another reason to not have Nazis fight alone, so that there’s no valour that they can earn alone. They won’t be able to capitalise on having fought.