I never got to try it, but was told that in pbr school. Their 61mm mortars can use our 60mm ammo, etc., etc., by design. Not that sure about the disintegrating links — they might have had to rebelt them. Could be wrong, too, but a lot of people thought it was correct.
It is a persistent myth.
Not related to the RVN stuff, but did read that their jet aircraft used the same fuel fittings as NATO for the obvious reasons.