Not regular. Only a few factions really use combat androids as troops, and as such they were fairly infrequent enemies.

I have never had to fight Ghor nor the other droid hunters, either. The one time we came at odds until now, he retreated without a fight when he learned I was involved.

[Missing the point so hard, Samus. And you only haven't had to fight Ghor because the Corruption plot didn't happen yet, give it time :P]