First of all I suggest you very very warmly to specify which Hardness Scale you are speaking about (there are different scales even in Vickers Hardness). Then please take into account that Yield Strength and Tensile Strength are strongly influenced by many parameters, even for a single alloy, even for that alloy in a given size, even for a single alloy in a given size in a given heat treatment condition.
Sorry, I have no expertise in Superalloys. i can just say that in alpha + beta Titanium alloys that relation is so bland that, for me, it is useless. Nevertheless there are companies that require hardness testing on Titanium materials.