Ok, dumb question, I know but... what's the rule on armor usage for heroes in Mordheim?

For instance we have mercenaries who can (presumably) wear any armor they find... light, heavy, ithlimar, gromril, etc

But what about shadow warriors can only buy light or ithlimar? Can the heroes be given heavy armor if found/bought after the first game?

Can any hero wear sea Dragon cloaks or just the dark elves?

Does ithlimar count as a kind of improved light armor?