Damn the vagueness of the negative psionic spectrum!
An untouchable shouldn`t have an aura, they are untouchable their resistance/immunity is confined to their immediate vicinity if not their person making it all but impossible to affect them psychically.
Their "aura" such as it is would only effect people is their personal space making them feel profoundly uncomfortable (thus untouchable.)
As opposed to a Pariah whose psionically negative aua projects a distance from them causing discomfort to blunts and outright pain to psykers making them unwelcome figures of unprovoked hatred and loathing (thus Pariah.)
As such unless you are all running around holding hands or driving around piled into a VW Beetle it shouldn`t be to much of an issue.