Currently normal moderators can set the moderators inbox to “Watching” the topics. In this case they are able to receive emails about posts ended up in the queue awaiting approval (based on the
notify about queued posts after site setting).
For category moderators, however, this is not possible. They receive the red notification on the site, but they will not receive any emails notifying them that there are posts in the queue.
Receiving emails as well as onsite notifications could encourage the use of category moderators instead of normal moderators.