Okay so I dug out my can of brake cleaner and it is safe for rubber parts. There is even a part on it that says ABS sensor safe. The same company makes another one for non ABS brakes. Personally I think it is the same product.

Anyway, the instructions do say that the rubber parts will swell but will return to normal after drying. I used this product on my calipers before I painted them and it sure does a good job of cleaning the gunk off. The spray is quite powerful and it blasted the dirt and grease away.

I would think that if a company made a brake cleaning product then it would have to be safe for rubber since most brake lines are rubber as well as the seals.