Update message:

UPDT:x:y:lemmings_saved:lemmings_out:job_id:x:y:z:i:j:k:...:num_updates:type:shape:x:y:width:height:...

So, the message goes like this:

UPDT - message identifier.
x, y - the position of the other player's viewport.
lemmings_saved - the number of lemmings saved by the player.
lemmings_out - the number of lemmings on the field.
Then, for each lemming out on the field:
   job_id - the string id of the lemming's job
   x, y, z - coordinates of the lemming
   i, j, k - lemming's velocity
num_updates - the number of map updates since last network sync.
Then, for each map update:
   type - the type of update. 1 for add; 0 for subtract.
   shape - the a string name for the shape of the update. Could be rectangle, or oval.
   x, y - coordinates of map update.
   width, height - dimensions of map update.

That should be all, I think.