According to these stories, the answer is yes, apparently the USAF used some in Vietnam:
Rick Schaefer writes:
"While at U-Tapao Air Base, Thailand (Sept. 1972 - Sept. 1973) [during the Vietnam war], there was a U-2 reconnaissance outfit stationed there also. The U-2 used outrigger wheels at the end of each wing while taxiing and taking off. Once the U-2 got enough speed, the wings developed lift, rose and then the outrigger wheels dropped off.
When it came time to land, the ground crew would run down the runway in a 1968 SS-396 El Camino to "catch" the wing tip before it lost lift and fell to the ground. I think, but I am not sure any more, that someone rode in the bed and secured the wing tip to the elky as the plane and El Camino slowed. At the end of the runway they would stop, replace the outriggers, and use the elky to tow the plane back to a hanger. I do remember that the El Camino was a well worn SS and that it took an amazing amount of co-ordination to recover the aircraft."
Guy Pegues writes:
"I remember watching an El Camino many times while at U-Tapao in '70 and '71. Strange watching an Air Force blue 69 SS race down the runway picking up training wheels!".
Don wites:
"My understanding is there were three of them. They were 350 horse, Turbo Hydramatics, with power steering. All of the normal black-out SS trim was in place, with painted steel wheels, small hub caps, and blue vinyl bench seat. The tops were white, and the body was actually painted USAF blue. All of the normal under-hood chrome was in place.
The U-2 only has fuselage landing gear. The outriggers (pogos) you saw are placed in pockets for ground usage and drop out when the wings have enough lift. Chase vehicles (pick ups) come in from either side and the wings rest on them until the pogos can be installed. U-2 pilots cannot see out of the canopy when they are on the ground, at least not what they need to see while taxiing. There is a periscope that looks forward, beneath the nose and that is what they look through. The El Caminos (now using Camaros) had all of the radio gear that was needed to communicate with the pilot.
If you ever imagined that the engine compartment was full, you should have seen it with two batteries, a humongous alternator, a/c compressor for the Kyzer roof unit, etc. Oh, no power brakes. I'm not so sure about the power steering thing, right now. It may not have had it.
I have a couple of pictures, but they're black and white. I had to keep it clean and ready for use, but got to drive it to fuel it and such. I was stationed on Taiwan at that time, and didn't go to 'Nam until '69. We were based at Bien Hoa."
This was found at http://www.chevelles.com/elcamino/ec_story.htm