If you look at photos of gents in "day attire" from the mid 20th century, you will see quite a few of them wearing tweed kilt jackets and the like with no belts underneath, and it doesn't look bad, INMHO.

I used to be very paranoid about always wearing a belt with a kilt, but now my kilt belt spends most of the time in my closet in a plastic tub. I prefer the "beltless" look, mostly because everyone else wears them!

A good tailored kilt doesn't need a belt to hold it up. But a waistcoat -- it adds a wee bit o'....wait for it...panache!

Cheers,

Todd