Does a turbine experience a countering electromagnetic force while it induces a voltage?
The turbine needs to develop sufficient torque to overcome the electromagnetic forces within the generator.

With a turbine alone, the hydraulic energy requirement would be to just rotate it at the desired RPM. To that would be added the energy required to keep the electrically unloaded generator rotating at the same RPM. The final addition would be the energy required to feed the electrical load, with the generator maintaining the same RPM.

The ultimate power (torque at the desired RPM), required to be generated by the turbine, would be decided by the electrical load.

The rate of flow of the fluid in the hydraulic system would determine the power that could be generated by the turbine.