I don't think its illegal to discuss smoking/growing weed anywhere.
No one is stupid enough to post pictures of their grow rooms online without taking due care and attention to ensure they're fairly anonymous, surely? ;-)
Hobby growers aren't the focus of anyone, where it is illegal its the serious growers / importers who are under the spotlight. And there are far better ways to find these people than scanning forums ...
Stick up a front page with a disclaimer, terms and conditions you have to accept to enter, cover your back, it'll be fine.