I didn't say the workgroup was the only thing that could be wrong. When you try to access by IP, does it ask for credentials or it just never answers? I would love to see the samba config for a system in that condition.
If you setup samba from scratch, did you ever compare the smb.conf that you created to the one OMV created? I don't even know how to make samba not work using the web interface. I honestly don't think there is a bug in the OMV config.
Just to confirm when you do \\ip it doesn't answer and same goes for the ftp service which were both enabled, I didn't compare configurations although I probably should have. I don't think this is an OMV problem or atleast not a web interface issue, even the graphs and view logs were giving me errors.