I see your speculation tag and raise you two speculation tags. Yes, it is.
(which is likely to be the stated reason for wanting the information).
This may be true. What I still believe is that the reason for wanting the information is that you can't enter into contracts with unknown parties. Logically the way to resolve this would be to tell everyone who identifies that they will be given X in compensation and ask them to sign a settlement renouncing any other claims. You need the people's ID to draft such an agreement.
I'm not better informed than anyone on the matter, I don't have this from Giga or anything of the kind, it's just my guess based on how one'd reasonably go from the lawyer's position (ie, trying to untangle this mess somehow).
This is surely not the case. GLBSE did not know the identity of the users, so this information cannot be used for authenticating the request against gigamining.
It's for the future tho, not for the past.