Hey Butch how about this one for your list.
Be able to set up and tension a speed line on the ground, and know how to use it. Little advanced for most ground men, but a good one should be able to set one up on the ground end if they have some of the skills already mentioned.
Variations to this would be a 2:1 MA system to help pull a big lead over, that one man would have a little trouble with.
Another would be to be able to set up a two way speed line with a retrievable pulley set up.
Another would be how to best set up the floating crotch, again using two or three ropes and a pulley.
In addition to what MM, Husky, Netree and others have said. I think what it boils down to on an individual basis, weather they climb or work the ground, one has to have a love and a passion for this work, because otherwise you just won't excel at it, no matter what kind of money your getting paid to do it.
Larry