From what I recall hearing in another post in this topic, wide guard only protects the opponent's team from attacks that hit more than one opponent.We also tried to test against Wide Guard in a Doubles battle, but it seems Wide Guard did not work in general. When we attacked with a non-Slip Through Pokemon, it still hit the target (who should have been protected by Wide Guard), and so obviously, the same target was also hit with the Slip Through Pokemon.
The only way I can see this being tested with Erufuun though is if it learned razor leaf as Monmen. And even then, that's assuming Razor Leaf can still hit multiple opponents.
Oh, and a question of my own to add to the list. Does Slip Through ignore Endure? I dunno how strict they're trying to be with "protection" but since it's on the same counter as protect and detect and since it does technically keep your pokémon from fainting from direct attacks I would think it's worth a test.