Why is the sump pump inlet draining directly onto the float?
Totally not a problem - if it was a problem, the sump would be overflowing and you'd be asking about the flood.

The force of a stream of water coming in from a side pipe to a sump is quite minor compared with the force of the collected water pushing up on the float. 

Assume that it DID affect operation - once the water had risen to the level of the pipe, the incoming water would be flowing straight in OVER the float, and the float would not be affected. But I bet it never even gets close to that point, in reality. 

If you like, take a 5 gallon bucket or a hose and dump/run water directly onto the float and watch what actually happens.