I wondered what FFG's take on corruption and Blanks was?

The GM in my campaign reckons they have no special resistance to Corruption but I would argue that as they ignore psychic phenomena and have a +30 against Warp Perils in addition to also having complete immunity to Corruption in the old version of Dark Heresy?

Also regarding the Psychic Null ability; how many times can they use it as Deny the Witch is an evasion maneuver which the rules can only be used once per round?

The rules also don't mention whether Blanks are affected by a Daemon's daemonic aura? I would argue that they are not or at the very least should gry the +30 bonus against warp perils.

I personally don't make Untouchables immune to all Corruption; there's more forms of Corruption out there than Chaos (think Radiation/Mutation). I do have them ignore Warp Shock and similar effects, however. They also don't benefit from those things that benefit you if you take Corruption (no invoking the Daemonic for them!).

My other house-rule is that Untouchables can resist Psychic Powers as many times as needed (they don't count against their Reaction limit, basically); if they end up staring down fifty psykers, they could conceivably resist every single one throwing a Smite at them (though the chances get slimmer with every roll). Some people think this is too powerful, but the drawbacks compensate as far as I'm concerned. I play up that horrible Fellowship in my games (the Tech-Priest with 20 has been cursing the fact that he has to talk to people so frequently).

I see and understand where Fantasy Flight came from in their interpretation of Untouchables; this brings balance to their mechanics, which helps keep a healthy game. Making someone Immune to Corruption is huge, as Corruption is one of the big threats in the setting (especially for the Inquisition).

I don't give Untouchables any special protection against Corruption. Corruption isn't limited to mutation caused by the Warp; moral corruption is a real thing and can affect the soulless just add readily add regular humans.

That said, Untouchables have several advantages that help them resist Corruption. They tend to have naturally high Willpower scores to fill the perquisites for their unique Talents, so they have an easier time resisting Corruption gains from many sources. They also have a large bonus to resist the effects of Perils of the Warp, which can often hand out lots of Corruption points at once.

The Untouchable in my campaign is an Assassin who cuts off the faces of particularly worthy enemies and stores them in a book as a sign of dedication to the Emperor. He has fewer Corruption and Insanity points than anyone else in the party.

In FAQ they say, that corruption is mind, body and soul. Blanks have a mind and body and those can be corrupted. As a GM you may feel suited to grant a bonus resistance to some sources of corruption, but that's about it.