Leave it as "fmserver". Set up other groups later.
Ok, so the referenced daemon group is a list of local users specific to the FM admin console?
If you install FileMaker Server for the local user you will be able to add databases to the data folder manually without the need to adjust the file privileges afterwards. This I find very practical for everyday server management.
Adding a user to the daemon group is easy using the Terminal:
sudo dseditgroup -o edit -a usernametoadd -t user daemon