Kind of major spoilers:
I don't see any reason why it couldn't be. I can't recall if there's any implications of Calbex's former squire being human, but the story implies that the squire died in some sort of traumatic incident involving the Aegis and the link between them and Calbex (ergo why he was so adamant about not linking with Corwan in combat), so presumably Corwan is the only human it could be.
My assumption about the story is that while it is about Corwan and his time as a squire alongside his pack, the ultimate plot of the story centers around the interactions and connection between Corwan and Calbex, hence only those two being on the title screen. Corwan seems to be developing a bit of a friends-with-benefits situation with his pack squires, while with Calbex it is a much deeper emotional story