If the question is about Pipe Bands, oddly enough, though the various Pipe Band Associations in the USA (EUSPBA, WUSPBA, etc) require Pipe Bands to compete in Highland Dress, the RSPBA (Royal Scottish Pipe Band Association) does not.

Bands are only required to be in matching uniform.

So, as has been pointed out, bands such as The Royal Army Of Oman Pipe Band and Breton Bagad bands and Spanish gaita bands, all of which wear trousers, compete (and sometimes win) at competitions in Scotland.

And British military pipe bands such as those of The Scots Guards, Royal Scots Dragoon Guards, etc have their drummers in trousers. (A clause in the RSPBA rules allows for the pipe corps and drum corps to wear different uniforms.)

Under competition rules in the USA these bands would be DQ'd.

Another interesting quirk in the rules is that a pipe band in which each member wore a kilt in his own tartan would be OK in the USA but DQ'd in Scotland.

So, a pipe band from Texas, when competing in the USA, must wear Highland Dress, but in Scotland could compete in blue jeans, Western shirts, cowboy boots, and cowboy hats, as long as the entire band matched.