No. The aunt cannot sign the form 8332.
The tax benefits cannot be split in any other manner than described under the special rule.
If the aunt has custody, you get nothing. The splitting of the child is only allowed between separated parents, as described above. They cannot be split between an aunt and a father. The aunt gets everything.
UNLESS the mother also lives with the aunt. Then the child is the Qualifying Child of both the aunt and the mother. The mother then gets to choose who claims the child. If she chooses the aunt, you get nothing and the mother gets nothing. If she choose you, you and the mother split the benefits, under the special rule and the aunt gets nothing. Obviously this doesn't work if the mother has no earned income to file a return based on; then you would get half the benefits and the other half would be lost.
