A xenos witch, possible corruption, yes. Perhaps even very likely, depending on how careful they are with their powers (The corruption is because they're witches, not because they are Xenos). Hanging out with non-psychic Xenos may make you politically corrupt (like taking bribes: see my various alignment and corruption tracks) but doesn't make you grow extra arms.
Also note that Alpharius is arguably the least warp tainted of the Traitor Primarchs. Corrupt politically, certainly, but has the least chance of becoming a Daemon Prince.
'Corruption' relating to political and social corruption should be different from 'Warp Taint'.