I agree with BillyZ's assesment, I might even put a 45* elbow on to direct the return water downward. But I would have it near the surface so you would not drain too far down, if the check valve fails.
I am not aware of any structural problems it might cause, but I would be concerned with power outage, even with a generator, sometimes power stays out for more than a few hours and generators fail. Say you never lost power though, the pump needs to be turned off from time to time regularly for routine maintenance. Fact is, Murphy and his law is in effect in reef keeping. If it can, it will, and you should plan on what can happen, not on what is likely to happen, IMO