When you look closely at the Shadow 2's frame, you will see that the checkering on the front- and backstraps stand out slightly, where on the SP-01 Shadow, they are receded. The difference is slight, but it is noticeable to some shooters, especially if they were used to an SP-01 with thinner aluminium grips.
To give a reference point, the difference between Double Alpha Aluminium Thick and Thin grips, is only 2.75mm, but that makes a big difference to the feel of the grip. Note that the standard Shadow 2 grip is already the flattest possible grip that can be fitted to this pistol.
You can, however, win a fraction of space in certain areas if you fit the SP-01 Shadow's grips to the Shadow 2 and this may provide a better grip in some cases.
When looking at the profiles, you will see that the SP-01 Shadow grip (in blue) differs slightly in overall shape from the Shadow 2 grip (in black).
The Shadow 2 grip is slightly longer from front to back, although this is a fraction of a millimeter and will not help you gain anything in the feel of the grip.
The top parts of the grips are also shaped differently - on the SP-01 Shadow it cuts away downwards, where on the Shadow 2 it is follows the shape of the beavertail. In this area you may feel a bit of difference with a different grip.
If you look closely at the below photo, you will notice that a very small stripe of blue is visible, especially at the top of the grip.
Thus in a nutshell:
PLEASE BE AWARE: