Two things:
I don't remember if this got answered, and can't find it thru searching, but was having the NPC equip a strapon removed? None I have found are ever interested in equipping it. I swear I equipped them on NPCs before.
And how do slave lounges work? My male playthrough has them in there, but my female file does not? Both have the same permissions.
If you are just giving them to the NPCs and they are not equipping them, that seems pretty normal to me. NPCs really won't ever equip items on themselves, but they will equip them on others. You need to equip the strap-on on them and after that they will use it, if they are interested in it.
I have never noticed any issues with slave lounges and I play as dudes, chicks, traps, futas, and herms. It's not to say that there isn't some problem with them, just that I haven't seen anything.
As far as I know, there is a chance that slaves will hang out in the lounges, as long as they have free time or are not sleeping. I usually see slaves in the lounges in the evenings between about 8pm and 12am. There is only room for 4 (maybe 5) slaves per lounge, so if you have more slaves than that, you need more lounges for them to occupy if you want to see more than just 4 at a time lounging around.