I was thinking of, for instance, a solid cabide end mill shank for a round cutter. Holding, on what might well be contact points only, might be a problem as clearly they are more designed for clamping in the likes of ER collets?
As for square I dont know, but with cutting forces down the length of the cutter contiuous cuts would present little problem provided the cutter did not slip in the holder.
Perhaps not needed if the crobalt cutters are as good as Gary suggests?