I'm designing an encounter with orks for my Rogue Trader group, but I am unsure how to treat the interaction of untouchables and/or blanks with orks, who don't normally exhibit psyker capabilities individually, but instead have a gestalt-type subconscious psyker ability. For example, if enough orks believe that missiles painted yellow will detonate with more power, then missiles painted yellow used by the orks actually become more powerful. However, those with the pariah gene (i.e. untouchables and/or blanks) have the innate ability to impede psyker abilities, just by be near the psyker.
Your answer can be summed up by:
YOU IS UN-ORKY! WAAAAAAAAAAAAAAAAAAAAGH!
Even a normal human in presence of a blank feels bit off. A psyker takes it to the next level. Imagine that you have to be close to someone who REALLY, REALLY stinks, to the point where your nose simply stops functioning - not very nice experience, but you can work around it.
Now imagine that you have a very sensitive nose and you rely on it as much as dogs. You are simply cut off from your main sense, which can cause mental trauma.
Back to original question: First of all, Orks are pure sociopaths by human standards; they see everyone as either an Ork or a target (and sometimes both). Let's assume that the ork doesn't want to immediately charge.
Orks other than weirdboyz are not psykers, even if they produce the psychic field that weirdboyz use as a fuel for their "magic" (and occasional head explosion). This is also probably the reason why Orks' teknology works: why guns made from metal pipe and duct tape shoot, why red cars go faster, and orks painted purple are harder to see (have you seen purple ork? My point exactly), etc.
If a blank suppresses the Ork's natural psychic field, then:
- Orks would feel bit uneasy, just like humans, and that would make them angry.
- A Weirdboy would be unable to use psychic powers, and that would make him angry.
- Ork Teknology would start to fail, and that would make everyone angry.
- Affected Orks would start looking for someone to blame and hit in the head.
Yasskier pretty much nailed it, however I would put a bit more emphasis on how many of the things the Orks rely upon begin to fail. Warhammer is open to interpretation, and has room for a lot of variance, some Orks use functioning tech, others use a metal box with loose screws rattling in it and no trigger. If your interpretation of Orks is of the latter variety, you can have a lot of fun with this situation.
Furthermore, you may interpret the Orks psychic abilities as coming from somewhere other than the warp, if that is the case, nothing happens, however, most people don't use that interpretation.
Some things will definitely happen, regardless of how you interpret Orks:
- Ork stealth would immediately and completely fail, unless these Orks are from the Blood Axes.
- All Ork Weirdboyz would begin to act even weirder than usual. At best, they'll completely but harmlessly lose their powers, and might actually become sane for a while. More likely however, they will being to behave erratically. They might explode.
- Any Ork of Nob category or above will actually get weaker. Whether that is by enough to have any gameplay effects or not is up to you.
- Cyborks will begin to suffer negative effects, while there may or may not be any immediate effect, over time their augmentations have a decent chance of shutting down or causing major damage due to rejection.
- Any Orks who have been stitched together in a particularly haphazard way will probably start to suffer negative effects, depending on how recent the surgery was. Surgery completed that day will immediately fail, the longer it's been since the surgery happened, the less effect the blank will have.
- All Ork vehicles and many Ork weapons will become less reliable. Whether this is by enough to have any gameplay effect is up for interpretation. If you choose to use this effect, the unreliable trait is a good starting point for this effect, though it should probably be made stronger.
- There will be a psychological effect, probably rage, however, you could get really interesting with this effect. Severe and immediate depression, uncharacteristic passive behavior, total anarchy as the Orks turn on each other, even an ill or high feeling could result from the sudden loss of the warp field. Most humans can't stand being around most blanks, Orks might actually enjoy it. The only guarantee is that they'll react, the exact reaction is up to you, and if in doubt, rage.
Whether these effects end completely when exposure to the Blank does, or have some persistent effect (especially the psychological ones) is up to you.