Well, you say that...
We do know if Sligs get paid. In fact they do get paid. Their wages originally would have played a huge part in the MO gameplay, you possessed Sligs, actually carried out their work and got paid - then you could go off to an ATM machine or weapons vendo, buy better weapons and armour and access to restricted sections of factories, and this was how you progressed through some parts of the game. Besides, how do you think Sligs become Big Bros? Random selection? Not likely - the Magog Cartel would only make the expenditure if they were sure the Slig could handle the equipment.
Yes, if Sligs don't do their job or violate the rules (or rather, if they get caught doing these) they have a report filed. This reports works its way through the Cartel until it eventually ends up with Skillya. Too many reports, and Skillya requests that that Slig come to see her, and then begins thinking about a new recipes for Slig Burgers, Slig Stew and the like.
Skillya may not be the most affectionate of parents, and the Cartel certainly doesn't tolerate lazy Sligs guarding their facilities (Sligs that aren't good at being security guards or soldiers are transfered to careers in admin, entertainment, journalism and 'personal slavery'), but they're definitely not slaves.