It really sucks when I post something and get no reply, so here is a reply to your questions!
#1 Yes, sometimes. They may climb in if the alarm has been sounded, but mostly thy prefer to run around. If a reinforcement spawns already in a vehicle, they will drive near you then get out. Sometimes though a guard will use the mounted gun on a vehicle.. "I'm going for the MP! (mg?)"
#2 Yes! And there are maps dedicated to the grapple as well! Often in obstacle/escape courses and Outposts. Keep in mind when adding them to your map, that if the falling animation occurs where your arms are flailing, you will look down and often miss your chance to launch a grapple. Also, you need to be at least 1 meter lower than the hook point to target it.