It all depends on what Cell South does to the phone. at the very least, the OS will be SLIGHTLY different since it doesn't include any of the verizon stuff.
You should know that 2.1 is not rooted for the droid. The rooting methods all exploit you going back to 2.01 and rooting that way.
If you can root your phone, I don't think that you should flash any droid roms to your phone because of those differences.
That being said, the rom's shouldn't be THAT different, so once an official root is out for your device, Cyanogen, Pete or someone like them should be able to make ports of the rom for your phone.
*Disclaimer: I am not a programmer, but generally, as soon as you put a phone on a different network, things are different enough that it's not cross compatible.