Well its been an iffy one. But the latest 40k main rulebook FAQ has still not cleared it up I'm afraid, like people seem to think.
Q. Can Psychic powers be used on a unit
embarked on a transport?
A. For simplicity’s sake, the answer has to be a
firm ‘No, unless the psyker himself is in the unit
being transported’.
The Doom of Malan'tai's ability is not a psychic power I'm afraid.
So there you go, feel free to check it out on the main GW website.