On a nice quiet airfield in Germany I took one piston ac down a Peri Track to 40 mph to check for nosewheel Shimmy - hard to keep the thing down!
Taxiing by engineers was quite normal, at least up to 2000, as I remember doing a C of A inspection on an aircraft in Jersey during an engine run and stepped out onto another part of the airfield. (WTF!...)
I have also seen one engineer wind down a Huey engine, lift the lever and give the pedals a bit of a kick to turn the thing in the right direction to tow it away. He was a bit of a nutter though.