Jimmi,
I think driving your steel pipes will be just fine.
Driving piles is a common mitigation technique to stabilize slopes. One way that dams fail is by one of the sloped faces slumping (sliding) downhill. Your steel pipes would actually help RESIST the slumping forces.
(One way to screw up, would be to auger your holes for the cement or sonotubes and then leave the holes open for a big rain. You do not want water going in the holes and then down to a weak horizon in the backside of the dam. Hopefully, you can just drive your pipes straight in - that is quick work on my property where the ground allows me to do that.)
P.S. I believe "rock chucked from lawn mower height" is a very important scientific measurement! Hopefully you can report your results back to Pond Boss after you determine that exact height.
