A portion of the fanbase thinks we've only been led to think it's Leo that is Salem's informant when in truth it isn't. Watts didn't mention the informant's name, only that they both knew Salem and Salem had told Watts about the informant's willingness to "comply."
We didn't see a face, all we got was a yellow robe. I'm not ruling out the possibility it isn't Leo, I'm only assuming it is Leo currently because we don't have anyone else in the picture at the moment. That could change when V5 arrives and we meet the new cast. Maybe it's not Leo who is the traitor, rather it's his wife or someone close to him.
There's also the idea that the Ozmite Headmasters, aka Dorothy's companions, have character arcs that are the OPPOSITE of their name sake's. Ironwood the Tinman is slowly loosing the heart he had, and Leo Lionheart the Cowardly Lion is succumbing to fear, in contrast to the TRUE COMPANIONS Dorothy aka Ruby. Weiss is the Tinman Stand-In, representing steel tycoons and industrial workers. Blake is the Lion Stand-in, a Scaredy Cat that fights for the disenfranchised and a William Jennings Bryan-figure. Then we have Yang which may be the Brainless Scarecrow, a representation for the common folk and farmers.