Every songwriter should know theory...that is a given....without knowing musical theory people will tend to make basic beginners mistakes and their writing will be one dimensional.
Regarding meter we do not need to know the tune of the song to work out its rhythm...that should be obvious from reading the words alone. It should also be obvious when lyrics fail to set out a meter or rhythm pattern.
Re putting down stress or beat marks...probably the easiest way is to make words or letters bold, in caps or italics to show where the beat goes. Dots can be added to show where long or short pauses between words are. Brackets (......) could show the bars.
All that said I personally do not see the need for all of this as lyrics should automatically show the songs meter and rhythm. Perhaps lyricists could provide a tempo eg BPM with lyrics to show the pace of the song. That might help with the music element.

Better still lyricists could learn to put a melody down and then we would could listen to the completed song on the MP3 forum without having to imagine a tune...just a thought.

http://www.soundclick.com/bands/songInfo.cfm?bandID=687727&songID=5238055