It all depends on the installation. Make-up air can come from many different locations and configurations. It should suffice to know that warm air rises.
If YOU want change, YOU have to first change.
If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!
Is it normal for warm air to be coming out of the makeup air vent to the outside?
If you do and there is a lot of air coming out then you could have leaky return duct located outside the building envelope ( like in an attic) and therefore positive pressure in your home which will then look for a way out.
The idea that this really is a makeup air vent doesn't sound right
You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!