Vault often fails to hook Privileges depending on the plugin load order, adding loadbefore: [Vault] to plugin.yml SEEMS to correct the issue.

Sorry I spoke too soon, the change I suggested doesn't fix the problem. I can only get Vault to hook Privileges by removing most of my other plugins. (though seems to only work in the presence of one of my other unrelated custom plugins)

Filed against Vault as well since the problem most likely lies in Vault-Privileges plugin. ticket is here: MilkBowl/Vault#360 with a bit more detail.

This was resolved in Vault