I think it was Diester that was ridden in a hackamore along with a running martingale. I have also seen long distance riders with this combination, so I would assume it is fine.
If u know anyone with The Complete Book of Bits & Bittng by Elwyn Hartley Edwards check out pages 99 & 100, 99 is a photo of Alwan (think I spelt that right) on Diester.