Depends on the Pariah - Omega Minus, probably. Somewhere a little below the Tau, where they dim a psyker's abilities, can't be read, and creep people out? Not so much.
And in theory a psychic apparation might be invisible to a Pariah - they would be immune to psychic illusions as much as telepathy. So, for example, a Pariah would never find a Daemonette attractive, where a non-Pariah would - he'd see the true, clawed and bestial and evil, form beneath...