Congrats on Eagle. I say his COH is his party and he should do it how he wants. I wear a kilt with my Boy Scout uniform on some occasions, usually for the summer camp golf tournament.
Maclaren is closely tied with boy scouts but of course I would recomend checking for your family tartan (for me Maclaren happens to be my family tartan ) but my first kilt I made for my scout uniform was OD green, everyone had to make a double take to know it wasn't scout shorts.
also :
http://www.nancynorland.com/cmsna/ar...hlanddress.pdf
may be of use.