Not sure what an "engineer boot or harness boot" is
I've not heard the term harness boot either, but this is generally what people refer to as an engineer boot (in my part of the world, anyway):



I have a pair of black engineer boots made by Chippewa. I usually only wear them if I'm riding my Harley Davidson. Personally, I don't feel they would look very good with a kilt. Mainly because of what the others have said: they tend to be 'open' at the top. Not snug with the leg, since they don't lace up.

But of course, depending on one's leg proportions and the height of the boot, it could very well be pretty close to snug at the top and look OK.