Topic on Talk:Zombie Panic! Source
According to the list of games which include the Source SDK Team Fortress 2 does not count, although there are definitely more games than HL2 that can be owned to play these mods. Is it possible for someone without any Valve games to test this by downloading the SDK from Steam and trying to play one of these mods?
Either that or get an outside source to confirm that these work with just the Source SDK? I'll update all the pages if we can figure that out for sure.