Why not? They have the same screen size and the Grip has a large hole for the camera which is situated around where the 925 camera is. Also the buttons are in the same place on the right...
The 1020 grip is designed for the 1020 phone, meaning that the curves and the actual grip along with the camera is made to fit the 1020 only. Common sense to be honest.
the camera grip fits in to your charger port, the 1020's charger port is on the bottom of the phone in the middle, the 925's is on the top of the phone and slightly off centre