Will a PWM-Enabled MCU Work With Any Motor?
Surely, the MCU has no concept of a motor and it simple outputs a PWM
  signal which can then be interpreted by anything (e.g a VFD).


PWM output from an MCU could be used with anything that accepts it. However some MCUs have specific features to handle motors such as bi-directional bridge drive, current limiting and fault lockout.

Different motors have different drive requirements. A brushed DC motor only needs one PWM output to control speed in one direction, but 3 phase BLDC motors need 3 PWM outputs as well as 3 other phase outputs and 3 differential analog inputs to monitor rotor position. 

If the MCU cannot do it alone then external components are required. When that gets to the point of being an entire ESC or VFD the MCU is no longer a motor controller, it's just a signal generator.