Interesting ... we would have never considered serving both sweet potatoes and red or gold potatoes (our go to's) in the same meal. On the other hand, we love both, so maybe we should try it.
Have you ever tried just thick slicing either a regular or sweet potato, microwaving a plateful for 5 minutes to soften them up, spray with cooking spray, season however you like and throw on the grill just long enough to brown up the outside so there's a bit of crunch. Yum! Instant french fries or sweet potato fries and so easy.
You can do the same thing without microwave softening them, but plan on longer on the grill - away from the heat at first, then over the heat to brown at the end. Yum!