Fae can allow themselves be seen, like how the centaur mailman allowed himself to be seen by Alice. Not sure if all fae can do it, but it would make sense for Titania, Spriggan and Oberon to be able to do so, being the royal group of the Faerie Kingdom.
I could be wrong, but I think it's mentioned somewhere that he has the gift of sight and that is the extent of his magical ability. It probably has something to do with why he was chosen to supervise Elias.
It's specified in chapter 51 that Simon was jinxed from birth so that any human who eats any sweets that he makes dies. Potentially he has the sight due to whatever caused him to be jinxed. However it is never mention in his backstory so he may have been granted the sight due to joining the church.