In the sense that you probably mean, i.e. connect a drive and have Windows Home Server manage the pre-existing data, no. Windows Home Server can only manage data in the shares you create using the server console application. Those shares exist on disks you've
added to the server storage pool, and disks added to the storage pool are formatted as part of that process.
You can connect a drive and manage the shares yourself, just as you're doing today. This is unsupported but not particularly difficult as long as you understand that the data on them is completely outside Windows Home Server.
I'm not on the WHS team, I just post a lot. :)