I'm a little slow at times, but I just realized that the suggested indented format is used for the Admin functions.
So maybe the same basic logic would apply to subgroups. The "Subgroups" tab would be a drop-down revealing the names of the subgroups. Then when one is clicked on, the tabs for it would be revealed indented further. So it would look like this when someone was on the home page of subgroup 1:
The advantage to this would be the user would see all the tabs available all the time, with just the additional subgroup tabs apparating when the subgroup is clicked on.