Ok the whole him being an undead thing would normally make sense given where he is, but the only reason he's undead is because of a curse from the Demon Lord that can be undone, otherwise he'd be a normal human who was revived from dead by the grace of their God and Grand Saint, so in this circumstance it makes 0 sense for them to treat him as a corrupted being (unless they somehow don't know about it despite them knowing he's undead).