Looks like the company I work is going to deploy a BES serer to compliment our Exchange server. If I use my Exchange email and the company BES do I still need the BWC I subscribe to through my carrier?
You still need to pay for a Blackberry plan, so you still need to pay that $40 per month. You just no longer need to access the BWC.
Theoretically, cellphone companies could provide a discount for not using BWC, and can provide you with a Blackberry-enabled unlimited data plan, then it would work. However, BWC is generally always included "for free" with any data plan you buy on a Blackberry. You still need your data plan.
You need to keep the BWC account with your provider. If you use a third-party MDS (such as myblackberry.us) you still need to be registered on the blackberry network, which only your BWC account through your provider can offer.
You're not paying for Web Client, you are paying for the BlackBerry Data plan, Web Client is basically provided free to the BlackBerry Data users. So you still need a BB Data plan even if you are using a BES, or the redirector.