Is there a way to differentiate in iOS mail notifications by account?
That is not possible using the default Mail app. It only allows you to differentiate between VIPs and regular senders (by placing a ☆ next to VIPs).

If you want to differentiate which account received an email within a notification, you would need to use a separate app for one of your accounts. You will then get separate notification settings for that app, and a different notification icon as well.