I wouldn't think you'd want to generate a 10VDC PWM to control them because 10V with what reference? If you have two different power supplies, they generate a voltage compared to their own ground wire so if the ground wires are at different potentials you'd get different voltages. What you want is 10V potential over the DIM- voltage, not 10V from a second power supply. Note that the datasheet says "additive 10V PWM signal".
Lucky for us, DIM+ is already 10VDC over DIM- and will source 0.1mA of current. That means all you need to do is use an optoisolator / optocoupler which is designed for exactly this purpose-- transmitting a signal between two devices on different power supplies. The two pins on the output side of the optocoupler goes to DIM+/DIM- and the input you just hook to a resistor and a PWM source, and the other leg to ground. An Arduino can source enough current to light the LED (in the optocoupler) to make it work, or you can hook that side to power (5V or 3.3V for an ESP8266) then sink the LED current into the PWM pin (which would invert the output).
I'm not saying that it couldn't work with some sort of MOSFET arrangement, but it shouldn't because DIM- and your GND aren't connected or at the same potential so it wouldn't switch and you could cause a whole heap of problems if you tried to directly connect them. I know others just stick an NPN transistor across it and power the base from a PWM pin, but that's really hokey because you're now pushing current into the driver's DIM- which is a bad idea*. EDIT: I would consider it a bad idea, but there are plenty of ways to make the 3-in-1 dimming work.
