By default, the BES 10 server is not set up to record texts however it can be set up to do so by the admin. I would imagine if it was set up to do so, you'd be informed of this beforehand and it would be a term you'd have to accept.
As for all your texts (Work and Personal) showing up in the Work Hub, that's normal. If your employer hasn't enabled the tracking and storing of your texts, they wouldn't see any of them despite what side of Balance they appear on your phone.
So.......despite it being technically possible for your employer to see your texts, you're right back to square one where you'll have to find out for sure if your IT dept. has tracking and storing enabled.