I wouldn't say that the heretics were good, but they certainly weren't shown to be evil. The problem with determining how to view them is that, aside from knowing that they wanted to stop the Great Journey, we aren't shown their motives. All we can assume is their short term motives, which would be prevention of firing the Halo rings and breaking up the Covenant.
However, if that had happened, what then? Would the Heretics continued the war against humans or not?
They can't be labeled as "good" or "bad" by the perspective of the humans because they were never aware of the Heretics. So the best that you could label them them would be an Anti-Covenant 3rd Party.