Paralleling output of multiple BLDC motors used as generators
Providing you use a 3 phase diode bridge for each generator, you can parallel the outputs with impunity. You should use the same model motor (with the same turns per winding/phase), mixing different motors will not work well. There will be no catastrophic results from this paralleling, simply a mismatch in current provided by each generator.   

Even with the same model motors, you will have potential differences from each generator, so the current/voltage from each will not be equally balanced. However since the motors have winding resistance this will help to balance the current from each motor/generator under load.

Providing the voltage output curves of the coupled motors are within a volt of each other you could take active control of the balancing. You could (if you can tolerate the losses) put a single high side diode on the output of each 3 phase rectifier and use a P-FET to partially short it out to even up the current flows. This could be driven by an analog signal or a PWM signal.







simulate this circuit &ndash; Schematic created using CircuitLab

You could also replace the three low side diodes with a FET and control the balance using those signals, but it's more complex.