A motor used as as generator driven at constant speed is more like a voltage source than a current source. It's therefore better to connect them in series, rather than parallel. However, once driven by something 'soft' like a wind turbine, that raises the impedance and you could treat them as either, so series or parallel should work just as well, as long as the drive is reasonably balanced.
However, there are some further considerations.
These motors can be used as generators, right? Permanent magnet motors, whether brushed or brushless are OK. While wound field motors, AC induction motors and switched reluctance motors can be made to work as generators with external excitation, they are not really for the amateur.
A BLDC produces AC. Put it through a bridge rectifier to get to DC before combining it with other rectified motors.
A series connection will put the same current through all the motors. If the motors are driven by different turbines, and one is shaded from the wind, you might find that one spinning backwards, which wastes power. Put a diode in parallel with each motor to prevent this.
If the generators are connected in parallel, then a shaded turbine will be driven up to the same speed as the others, again wasting power. Put a diode in series with each motor to prevent this. The rectifier for a BLDC already provides this functionality.