I would think that those sources would be decent sources for pretty clean rain water to be fed to the pond.... In my opinion, I would prefer my pond be fed clean water from off of a roof and / or ground water from a sump vs. runoff the from a field with possible chemicals contaminants etc.. so no problem with that as i see it.
Do you have a transit / laser level to confirm elevations? The way I see it, the sump pump is going to be able to pump into the pond no matter what level the pond is at..... The check valve will always prevent backflow. Now with that said, check valves and sump pumps do fail so it would be good to verify elevations in case it fails during a flood or you have to change out the sump pump during a flood.. As long as the gutter downspout entry point is higher than the pond water level, the water will go to the pond... if they are not, then they back up, fill the drain tile around the house and at that point the sump pump would be responsible for all of that water plus any other ground water.
I'm not expert but that is my thought
