Yes. Whimsyshire drops the same loot as acts 3/4 of the same difficulty that you're on.

This means that Hell Whimsyshire will drop iLvl 61 and 62 items at the same rate as Act 3/4 will.

Yes. Whimsyshire drops the same loot as act 4 of the same difficulty that you're on (except for inferno which drops loot of the same quality as acts 3 and 4, which have the same drop rates).

This means that Hell Whimsyshire will drop iLvl 61 and 62 items at the same rate as Act 3/4 will.