Can an Arduino Micro receive commands from another microcontroller when hardwired together?
You cannot do this with the micro USB ports.  You will need to use I/O pins.  Either serial or I2C would be good options.  It might be advisable to use I2C if you want to control multiple 'slave' microcontrollers as they can all sit on the same bus.  Using the serial port would require multiple transmit and receive pins on the master controller, likely requiring software serial ports (high overhead).  Also, if you don't use the serial port for comms, then you can use it for debugging.