The distortion caused by shape of the tank will not affect the light output in anyway other than the fact that the shape makes it a little more difficult to make a lighting plan that works with a rock structure.
One of the hard parts of round tanks, bowfronts and tanks of that nature is the viewing. You will get distortion and odd angles BUT that is part of the pleasure too. I have a corner bowfront and enjoy sitting up close and looking.....
Taking pictures is also difficult. I have to move corals to the front glass if I want a very good closeup....otherwise the distortion makes it difficult to get everything in focus...even with a good camera.