Native American designs can be very similar to Celtic designs and very different. I'm not saying they have to be "Celtic looking" to be worn with a kilt, to the contrary it could look very good. Riverkilt has blended the two cultures in several of his photos (vests, sporrans, kilt pins...)

I'd say try it and post some pics. Some designs may look better than others and we can provide you with more helpful feedback.

The kilt is such a versatile garment. From formal wear to casual, or can be worn with many more colors thanks to the spectrum of colors in the tartans. I believe it can also be blended with many cultures if the blending is kept in balance. That balance is relative to the individual and based on perception. Give it a try. If you don't like it, you can always modify the look