Essentially this is what I am trying to do:
. Delegate tasks to teammates
. Have them receive Tasks
. Have them update status of Task
- notes, attachments, etc
. Complete Task and check it off as complete
. Have entire team aware of open Tasks via OmniFocus
Something like Trac (http://trac.edgewall.org/) or RedMine (http://www.redmine.org/) etc. will do everything in your above list and then you can use an AppleScript running locally to pull and push tasks to OF. There are scripts on the web that do this already. Sure it's not ideal but it would be fairly simple to set up.
I've just noticed OF doesn't have a Scripts menu. That might be a good feature request. If you could run scripts from inside OF, that would make this sort of thing a lot nicer.