I would STRONGLY recommend not encrypted an SBS server. Trying to run Exchange, AD, DHCP, DNS, SharePoint, all that stuff on a single box makes SBS installs struggle at the best of times. Adding an encryption layer to the top of that and you're asking for a lot.
You need to ask the client what the purpose of whole disk encrypting a server that's always on. All the data is freely accessible to anyone who has phyiscal or network access to the server, you aren't protecting anything.