The Cellular South Milestone/Droid is the Droid A855 re-branded for regional carriers and given a model number of A854 to differentiate. Aside from the name change it also has a baseband which does NOT lock the data settings to one specific carrier.
DO NOT USE A RADIO UPDATE FROM VERIZON!
So long as you avoid using any SHX/SBF files from Verizon or update.zip files for updating the radio you should be fine. Any reputable ROM developer will have radio updates separate from their ROM so you should be good with any Droid ROM through ROM Manager or on this forum.
Also, you will need to add a custom apns-conf.xml file to /system/etc/ or an apns.xml file to /system/etc/customer/ in order to enable MMS on any third-party ROMs. You may want to check for and pull these files from your stock ROM before you start messing with custom ROMs.