In my opinion it would be very useful if the visibility of JIRA-comments created by the scm-jira-plugin could not only be restricted by role but also by group.
The problem with visibility by role is that for any project and any user commiting to this project, the user must be member of the role in this project. For large scale Jiras with some dozens of projects and changing contributors this is rather hard to maintain.
I suggest that the configuration of the plugin should have another switch to determine whether the name typed in the "Role Visibility" text field is meant as a role or as a group.
I also had already a bit of a look at the source code. As far as I see the necessary change would be just depending on the state of the suggested switch to set
the private final String type = "role" in \src\main\java\sonia\scm\jira\rest\RestVisibility.java to "group" in case that the plugin is configured to use visibility restriction based on group.