If you use BIS for company email, then no they cannot see how you use the device and what you send/receive.
If you are using BES for company email, then read this:
What can a BES Administrator “see” on my BB...
What does BES see; what can be tracked/logged? - Port3101.org : Your BES Connection
I never recommend using a personal BB on a company BES. If they want you to have email access, then they should provide the device.