It is unfortunate, but the dress code is clearly stated

Young Gentlemen —You may enjoy wearing a tuxedo, but it is not necessary for this event. Dress pants,shirt, and tie are perfectly acceptable. Avoid jeans, shorts, sagging pants, or t-shirts.

So, it would seem dress pants are expected and we should not simply assume a kilt would replace them. I agree it does not say not to, but it does state 'pants'. Now, if it said formal, semi-formal, smart casual or other less specific to garments we might see some latitude for the ethnicity of dress the young fellow wishes the organization would tolerate. Having read the site, I think he'll be waiting a very long while.