According to blizzard, immortal reduces any incoming damage to 10 as long as its shield is activated. Does it mean that when the immortals get nuked, do they only take 10 damage and survive, or do they die as this is an exception?
I've tested nukes and they deffinitely are an exception. Not tested yamato, but I think Makki is right about it too...
Hunter seeker missile does not effect it, I believe its things that don't have single fire attacks, I mean auto attacks, that it will not work against.
Immortal hardened shields only activate against regular attacks. Any ability (psi storm, nukes, yamato cannon, 250mm strike cannons) will ignore it.