Yes, they can appear in the Great Vault. They’re obviously not SUPER common, but they exist.
A close friend of mine, who plays Resto Druid, got a 489 Nymue staff in her Vault and it’s a Very Rare piece:
Another friend who got this in their vault on their Priest alt:
And in the last three weeks I’ve gotten a Normal Dreambinder, two Volcoross necks (neither of which I took), and an Augury (which I also didn’t take).
Ashkandur isn’t a very rare item. But yes, it could drop from your Vault last season.