RE: onyx bl system...??
Yes, you can run NiMhs on a brushless system, won't hurt the system, but it WILL hurt the battery. NiMhs just aren't designed to dump current like LiPos can, and the NiMh battery will get hot. Heat is bad. It will eventually kill the pack. But, I suppose you might as well use them until they're dead (unless you have a friend who's still running NiMhs).