As a thought experiment, consider if we developed a drug that makes humans enjoy slavery. Would slavery then be morally acceptable, provided that drug was furnished to the enslaved humans?
It's not directly relevant. If we don't build unhappy robots there will not be any unhappy robots and no potential for any extant robot to be unhappy.
Not two classes (with or without pill), nor a history of previously unhappy robots (pre-pill), and not even potentially unhappy robots (pills run out). Only happy, working robots.
