RP servers do druid guilds, but PvE and PvP guilds tend to just throw a 40-man druid-only Onyxia raid together now and then, or something like that.
I've never seen the whole Team Druid phenomenon with any other class. I sometimes wonder if I see it just because old HoJ had it, but then I come across a video of that Ony raid, or pics of dozens of druids flying over Shattrath, or lining up against the dome wall sitting down in bear form. Or my personal experience, the night before they did away with tree form: a whole lot of druids danced in tree form on the steps of the Horde bank in Dalaran until the server went down for maintenance and DCed us all.
I can see it happening with troopers though, if they can handle all roles. If people are willing to form Imperial companies in the real world, they're surely willing to do it in SWTOR.
"No Sith were spared in the making of this video." Nice one.