I don't mind HOB's for QT and hostpital tanks because you don't want live rock in those as it can cause problems. For example it can be a place the parasite you are trying to fight hides and infects future fish that get in there or if a fish is infected it can flash against the rock and harm itself so in that case a power filter is really the best option. As for clean up crew I don't keep a very large one by most people's standards.