Those seem like big holes to me. If the holes are clogged, the gravel won't get in the pit. If the holes are clear, you're predicting some very dramatic erosion. Seems like a stretch. If the holes are low, it'll take in more water - that should be good for the floor. I think sump pumps are made to run continously for some time. The cold water is all around it and running through it. That should keep it cool, yes? That said, I'm not sure how the height of the holes, relative to the float, will have a significant effect here. When I see something out of my comfort zone I usually start thinking of sky-is-falling worst-case scenarios. Take a step back. If you're confident what you're seeing is a problem, pursue it or do more research.