If you buy your scar vet the Sword of Biting and are armed with a great sword is it a great sword of the biting and no problem?
If you have a magic weapon and a mundame weapon you have to use the magic weapon, if you have any weapon but a hand weapon you would have tou use that too. (spears, halbreds)
So the only way to have my scar vet using a great weapon is to forgo a magic weapon. Thanks. This is a decent alternative for if the scarvet has the BSB and can't get a magic item he can have a great sword instead.
If you're worried about having a magic weapon (to fight ethereal enemies, for example), remember you can use Veneom of the Firefly Frog on that Great Weapon. Then you have magic, poisoned, S7 attacks.