You can use the chainring, but each brand (Shimano, SRAM, etc...) aligns the shifting ramps and pins to work best with their own brands inner rings. So the indexed shifting will not be as fast/smooth as when you would use the same brand of rings together.
Inner rings frequently have individual teeth shaped so that the chain will lift off and drop down faster in certain positions. These teeth are lined up with the ramps and pins on the outer ring, to facilitate faster/smoother shifting. If you pair a SRAM outer with your Shimano inner, these teeth will not line up correctly. It won't make the shifting not work, but it will just not work as well. The X-Glide road rings are also designed for 11-speed, Yaw front shifting; your're paying for tech/features that your bike can't fully utilize.
Also, you are right, X-glide rings do not come in 50T, 130BCD combinations. You'd have to go with a 53 or larger size.