Terminators may be able to cram in in emergencies, but that is like, if they have to evacuate an area, don't have teleportation available, and have to move because a gigantor rok is going to fall on their base in half an hour.
In battlefield conditions, they don't rhino-ride because they are as you said, difficult to get out of, and it would not serve them to be fumbling to get out when there's twenty krak missiles headed towards their transport.
Erego, in terms of actually playing 40k battle, they can't. Though, from a fluffwise perspective, that is an interesting and slightly amusing thought.