So the Hardy Talent says that a character with this talent treats damage as lightly damaged. Is this in regards to heavy damage or for ALL damage- including critical damage.

I consider it a very good talent and I treat it RAW.

Yes, Hardy makes sure you ALWAYS count as lightly wounded.

The talent says: "when undergoing medical treatment or healing from injures he recoverers damage as if lightly wounded" (p. 99).

So for the purposes of the effects of a medicae test or natural healing from rest: yes it means the character is always lightly wounded.

BUT for the purposes of the effects of damage in a battle, the character is not immune to the effects of critical damage. The tables for critical damage still need to be consulted and he can still loose a limb or see his head explode or whatnot.