So that's what those are for

Regarding the slave recepticles, the new standard NATO recepticle isn't the same as the old 2-prong type used on the A1, Gama Goat, etc. The new ones look the same on the outside, but the 2 conductors are concentric, instead of side-by-side. They could (and can) be used for jump starting, charging or running auxiliary equipment. There is an adaptor made to connect a new cable to an old style recepticle, and vice-versa.

As far as the M151 MUTT being a Jeep or not, most say no. I for one think they are, as they were the main "Jeeps" we ran during the VN war, and the original design was by Willys! They were later built by Ford, then by Kaiser, AM General, and GM. Pretty much like other military Jeeps. There are still a very few M151's in service in Korea, as well as a few other military installations around the world. At the start of Desert Storm, as logistics were being worked out, some bright fellow realized that the Marine cargo helicopters picked for the first thrust wouldn't fit a HMMWV into the rear bay! A few phone calls and a few days later, the troops ready to load found 50 M151A2's lined up on the flightline.

 

Well, I can speak from experience as a maintenance test pilot. I made a slave cable that hooked up to our aircraft to a HMMWV (Hummer). I use it to charge batteries, troubleshooting, and other tasks. However, I would never try to start the aircraft off of it as the load would be so much it would likely damage the charging system on the vehicle or would only provide an initial start and would likely drop below required battery power needed to complete the start. Keep in mind my experience is solely based off of helicopters. I am not sure what the demand would be on smaller aircraft.