I don't know anything about the kind of work you are doing, but it sounds like the kind of work wear you might not even be allowed to wear shorts?
When I worked for grounds maintenence at my university, due to safety regulations, we couldn't wear shorts even when it was very hot. Although my boss was very cool and understanding, I am sure that if shorts are not allowed, that kilts would not be allowed either.

I agree with everyone else, that keeping your job should be your first priority.
However, I think that everyone is making a bigger deal out of this than it has to be.

The easiest way to find out if it is ok to wear a kilt to work is to ask. Though, I would not suggest asking directly whether or not you can wear a kilt out of the blue.

I would suggest asking your boss what the dress code is. Don't ask if it is ok to wear a kilt right away, just ask what the dress code is. If a kilt seems to fit with that dress code, then say something like "So, a kilt would be ok then?" and if a kilt seems against the dress code, either forget about it, or just to be sure say something like "So I guess I can't wear a kilt, then?"