If you could get the spring to flow on the surface and into the top level of your water, I wouldn't worry one bit about it. Otherwise, place the pond down hill of it. You may need to seal the pond basin really good, because you may hit some vein of that spring, but that shouldn't be killer.
I would ask your pond guy more questions. Does he think your scenario will cost more than normal? I would think a pond dug into a hillside would be cheaper than one that is not. You have a longer dam, but that dirt that comes out can be used for that. Not as good as a small dam in a ravine, but sometimes those have issues with creeks, water rights, etc.
