His fellowship is halved, and he takes an extra -20 versus anything with a psy rating or the psyniscience skill [he's quite uncomfortable to be around, moreso for them]. So for regular normal animals the fellowship's already doing the job. You can 'show' it by how they act around him, but he's not more prone to them attacking if they aren't psykers in some way, than anyone else with the same fellowship score [and probably no social skills].
As for immunities, he protects a small radius around himself to the tune of -[Trait] psy rating: this will affect accuracy and maximum output of nearby psykers or ones firing at those within the field. The untouchable himself is outright immune to Psychic and Warp effects. Any ability of a Daemon, Warp-Weapon qualities, psyker powers or sorceries or rituals, it just doesn't work. Even inferno won't affect him, despite the giant flames.
I've not read the adventure, but if the blood-drain is physical, like a leech or giant mosquito deal, that will work just fine. If its any sort of power or supernatural ability its going to do nothing. Simply fails. Its not instant but it won't be long before they figure out what the problem is. He won't show up on warp-sight or psyniscience which is a dead giveaway when they take a look.
Entities can still converse with him and all that. Posession and the like wouldn't work, nor would telepathy, but if they can just speak or write, that would work just fine. Not that any warp or psychic entity wants anything to do with the guy.
Rituals though, that gets screwed up FAST. If you can sneak the untouchable into it, things ain't gonna work. Worst case scenario throw him at the main caster or portal or sacrifice and watch their plans go wrong.