Aye, they also share the same battle music. I always liked to toy around with the idea that they are one and the same. When Volvagia was defeated his body burned up and left nothing but a skeleton, that's what made me think of it. Then I noticed the music and was like... "Whoa! Maybe I'm on to something..."
As for the slight differences in appearance, I think that can simply be explained by the different art styles. Most enemies look completely different in each game. So yeah, I believe they are the same.
EDIT: How it ended up in Arbiter's Grounds? Zant probably transported it there to destroy Link. Another theory, assuming that they're
not the same entity, is that in life it was some sort of beast used to execute prisoners, but one day it got out of hand and the guards were forced to kill it. That explains all the spears lodged in its skull (yeah, the spears are one thing that make me think it might not be Volvagia).
But at the least, its a reference to Volvagia.