Well its a balance really - capacitance at the motor terminals really will reduce interference - so long as this
isn't too large its not going to overload the driver circuit (but you have to do the maths and/or measurement
to get the best value). Remember the leads to the motor have some intrinsic inductance and that a little capacitance
in the right places can moderate the high speed transients.
Perhaps a simple rule of thumb is try capacitance at the motor terminals thats about the same as the drain
capacitance of the driver MOSFETs - that way you are not loading them drastically but you are shorting out
RFI at source and reducing the radiation from the motor leads.
Monitoring the amount of interference with an AM radio tuned between stations can be very educational, BTW.