My two cents for what it's worth (and someone with more fashion experience than I have please correct me if I'm wrong, I'm still learning):

I think the answer is going to be heavily dependent on the kilt itself (what colors is the kilt? is the kilt wool, pv or something else? is it tartan or solid? is it traditional or contemporary? where will you be wearing the combination?) and the over-all "look" you're trying to put together as a whole outfit.

I like that waistcoat. But it is a very strong garment. It's boldly colored, styled and patterned. It's the type of garment that is normally worn as the focal point of an outfit by itself. I'm not saying it won't work with your kilt...just that the role that particular waistcoat appears to fill is one also frequently occupied by the kilt.

I think knowing whether or not we think they will blend well or clash is going to be pretty dependent on seeing the kilt itself in this case.