In a nutshell:

• SP-01 Shadow grips can fit on a Shadow 2 and vice versa.
• Although there are small differences, it doesn't phase most customers (even very particular ones).
• Most aftermarket grips are made to fit both pistols.

Shadow 2 grips compared to SP-01 Shadow grips.

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.

When looking at the grips, 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 a fraction of a millimetre may or may not be noticeable to you. 

The top parts of the grips are also shaped differently - on the SP-01 Shadow it cuts away along a straight line, where on the Shadow 2 it is follows the shape of the beavertail. In this area you may feel a bit of difference between the two grips.

If you look closely at the photo below, you will notice that a very small stripe of blue is visible, especially at the top of the grip.

Note: SP-01 Shadows come standard with pan head screws, while Shadow 2s come standard with countersunk screws. Whichever grips you are fitting to whichever pistol, please check whether the grips come with the appropriate screws and if not, whether you already have the correct screws or if you need to order it separately.