I don't see anything wrong with advertising. People advertise where they know the ad will be seen.
The FOC teams knows ESF is popular, therefore they get a flunky to post information in the ESF forums, where they know it will be seen.
Really, it's the smart thing to do, making sure that people know about your work, so it's not done in vain.
Although, it's not always accepted, and can be considered rude to post about a rival mod in a mod's forums.
What I'm trying trying to say is that there's nothing really wrong with posting about FOC, DMZ or the other thousand DBZ mods out there, it's just kinda rude doing so.
The saying "Don't be steppin'" works here.