I don’t think so. Mention notifications ("notification_type": 1) are meant for the specific case of when an @username is added to a post. Using the same notification type for direct replies would cause confusion.
There’s an edge case to be aware of. If a username is added to a reply to a user’s topic, the notification that’s sent to the user will be "notification_type": 1, not "notification_type": 2. For example, by mentioning your username here, this post should trigger a notification telling you that I’ve mentioned you, and not a notification saying that I replied to you: @MarcP.
Note that if a user other than yourself was watching this topic, they would get a notification with its type set to 9 (posted.)