Transfer Function Conversion
I am trying to calculate the effects more accurately, so I use the
  equivalent circuit for the motor to derive a transfer function which
  is then put in parallel with the filter components with the clearf
  goal of reducing it all to one R one L and one C which then allows me
  to calculate things like the -3db point


Why don't you just draw the LC and equivalent load of the induction motor as a circuit for a simulator then ask the sim to do an AC analysis.

The formula you derive will be complex and you should forget about your: -


  goal of reducing it all to one R one L and one C


Because it won't happen. Use more appropriate tools.

On another point you equate the induction motor TF to be: -


  Z1 = Rs + sLe1 + sLm*(sLe2 + Rr)/(sLm + s*Le2 + Rr)


But I see nowhere in this equation the resistance that represents the mechanical output of motor and slip-factor.