You don't need to place the BES in the DMZ, just the Router has to be there. The Router will connect to the outside and the BES will communicate to the Router through 1 port. It's easier then setting up your Exchange to use static ports.
Also, if you have issues and call RIM you will be out of luck as it's also not supported.
If you change to static ports the BES doesn't care as long as MAPI still works. It's Exchange and Outlook users that will suffer the most if it doesn't work.
Remember that BES is just like Outlook, if MAPI works then BES/Exchange/Outlook works. If MAPI is screwed then so is the BES/Exchange/Outlook.
Here is the KB about placing the BES Router component in the DMZ: BlackBerry Search Results
This might help with the people in your company. Just tell them that if the BES goes down and they want to call RIM for help that they may as well set the BES on fire.
Set it up properly and you will be fine, but it's up to you and the people in the company.