When you say "non-active" do you mean marked as unplayed, but as one of your households in the household manager? In that case I think the game just doesn't cull them, but otherwise treats them as unplayed.
If you mean a played household that you're just not currently playing at the moment, they will age if aging is on for played households, but they won't advance in their jobs (they won't quit them either). I think they can continue to gain skills, but if for example Bob Pancakes is in the chef career and you see him in the park using the bbq, he is probably gaining skill from that, but Bob isn't going to go home and focus on learning to cook and increase five levels by the time you rotate around again. If they're offstage while you're playing another household, they are essentially static, yes.
For the record, I played with a large rotation with aging on for only the active household for a long time and I never had sims gain (or lose) levels in their jobs or gain significant new relationships without my intervening. They still might meet other sims and have opinions about them for whatever reason. The biggest job related annoyance is that they don't go to work if you're not actively playing the household, so if you happen to rotate back to their household in the middle of a shift they'll be late to whatever degree (same thing for schools - kids will be at home or wherever you left them when you last left the household).
