Being a Dane I'm very sensitive towards horns on vikings, but with the Jomsvikings I would actually like it. They are an Elite, supermen, Kensais in groups... They have damn well deserved the horns, which actually look good on them (but how should a person ever be able to wield such an axe?).
I jst hope the rest of the vikings don't have horns.

And the Sherwood Foresters as far as I have heard are an Early unit, not a VI unit. And since the Jomsvikings are from the sagas, which can be said to be little more than legends at times, well then the Sherwood Foresters need to be there too as they are from the legends and then some.
BTW, I have heard that Robin Hood is in the game as we know it now, a rebel in Wessex or Northumbria. Should you bribe him and give him a title he will become Lord of Locksley.