It seems the issue was a permissions one. The folder on the mirrored RAID did NOT have the right permissions. "fmserver" needs to be owner with read/write privileges, and "fmadmin" needs to be a group with read/write privileges. In ServerAdmin under Sharing, you might want to proprogate permissions down from you starting folder name (i.e. foldername1 in above post). Now desired default databse file path validates without a hitch.
One other thing that has bitten me: When you create a new file on OS X (like if you compact the database), make sure you update the file permissions before loading it to the server. It won't automatically add the extra permissions. It'll host, but you'll be left with a file you can't edit. A situation that potentially can create confusion and four-letter words.