does it matter? the character he voices isn't in the game so I do not see the need for him to be one of the va. If I were to be subjective to my experiences though I'd say I don't enjoy the voice hayter brought to the tale anyways.
He voiced Big Boss in MGS 3, Portable Ops, and Peace Walker, so it's still "his" character.
They're probably changing the voice because they want an older sounding Big Boss, as they did in MGS 4, but I could understand how he might feel snubbed.