I'll offer a different opinion. If made well, and really form fitting to the leg, I see no reason why traditional cadadh, tartan hose cut and sewn on the bias, cannot work with modern Highland formal wear.

I will stress the "made well" and "well fitted" aspect, however. I think if made poorly, or if they are ill fitting, the look will be sloppy. But if done right I think it would look fine.

Adron Britt, who makes the Ferguson Britt line of sporrans, is excellent at making his own cadadh and frequently wears them with his kilts. His are so well made I don't think many who see him wearing them realize that they are cloth hose, not knit!

On the other hand, I've seen some reenactors attempt to make cadadh and it has ended up looking like they have simply stuck their foot in a tartan sack.

But if you know what you are doing and make them well and well fitting, I say go for it!