I'm not sure what they're for, either. At the default XP rate over time (10+ on 2d6 once per month), it takes years to get them to qualify as anything (after which they can finally start earning XP in some role or other). And are you then supposed to mark them as not dependent anymore?
AtB does not seem to be dealing with them in any mechanical way other than to have the fill up the save file and draw salaries?
That said, if they don't count for your astech pool, something is wrong. Note though that 'bring all astech teams to full strength' does not remove astechs if you have more than you need, it only adds them if you're short. To get exactly what you'll need you have to first 'release all temporary astechs' and then 'bring all astech teams to full strength', at which point the astech dependents in your roster should be taken into account.