Looking for a set of winter rims for the X3 (2008). Which I am having a hard time doing so..

To my understanding what's on the vehicle now is
17x8J
46mm ET
5x120
M14x1.5.

I found a very good deal on a set from a 2012, 535..Looking the wheel specs up;

17x8J
30mm ET
5x120
M14x1.25

The ET throws me off. What does this mean will the tires basically be inside the wheel well too far? Will it even work? The winter tires I am putting on are 235/55/17.