I think it is better if your uncle start the process for visa once he actually gets his Green card. The law says that once your asylum is approved  you can only file for Green card (Permanent Residence) after 1 year. And it takes about 3-4 months to get Green card if all your information is correct. So, I suggest him to wait. Or else he can apply for an emergency travel document to go to India and meet his mother there instead.