Personally I have never used JUST an air conditioner. As such, I have always needed to use an exhaust system in order to remove the hot air. Already stating that I have never done it, I can't say if it would work just using an air conditioner with no exhaust. Others on here seem to say it will work. But personally I wouldn't recomend it. If you are bringing fresh air in, how does the old air get out? As a general rule, I look at my ladies as ... well ladies, and not as plants. I put myself in the same situation that they are in and ask if I would like it. Option A) a small room with moderate warmth, not too hot, not too cold, plenty of nutrients, with fresh air .... or option B) same as above, only istead of having an open window just having an AC unit. Personally I would choose option A to live in, but that's just me, so that's what I subject my ladies to. Again, just me.
As far as I know, scrubber and filter can be used interchangably. And no, it doesn't have to be hooked up to an exhaust fan per say. You only need to get air to pass through it. Exhaust fans seem to work the best, but I have seen pictures of people taking $10 box fans and ductaping a home made scrubber to it, and have heard it works fine. Again, I never have done it, only heard it works. As long as you get the stinky air to go into the scrubber/filter then the clean air will go out.
If you are worried about parental visits, as long as the scrubber/filter isn't self contained in only the grow area (i.e. a box fan with a cardboard scrubber attached to it, sitting in the grow room and taking air from inside the room and moving it through the filter then putting it back in the room) then you should be fine. But that's just what I think. I perfer to shell out the extra $$$ for profesionally made carbon scrubbers with profesional exhaust fans. Just me though. I figure it's alot less expensive to spend $300 on a professionally made carbon scrubber and fan than it is to spend $25 on a home made one, then the additional $1000 in lawyers fees, $1500 in court costs, and $3000 in fines once I get caught with it. To me, I'd rather spend the $300 than the $5525. But maybe it's just peice of mind I'm paying for. Either way I'll take it.