Scotty always wore a kilt with his dress uniform in the original series. After that he never wore it again. As one of the pictures showed, James Doohan did end up wearing a kilt in the same tartan years later.

That one on display is not from any Star Trek but is probably someone's attempt at what it would look like. I think it is a shame that at Spock's Funeral they did not have him in a kilt, as I think it would look great with those red jackets they wore in that era.

At the risk of revealing myself too much of a geek, I have a red dress uniform tunic from the original series that I bought specifically to wear with my kilt. I do not wear it often, but when I do there are more knowing nods of approval than one would think.