There is no communication between the controller and the drive. The only information that is being sent to the drive is a digital pulse (in the case of stepper motor) or an analog voltage (in the case of a servo). There is no communication back except for encoder pulses and digital line states.
That said, I can imagine a scheme where you created your own communication. You could use the digital (trigger) lines to specify the type of drive. You could always set bit '0' high when using a stepper, and always set bit '1' high when using a servo. Then in software you could read the two bits to determine what - if anything was connected. You would get the following:
Read bits Meaning
00 Nothing connected
01 Stepper connected
10
Servo connected
11 ERROR (both connected??)
I haven't worked out all the details, but you probably get the idea. The only problem with this scheme is that you have to configure the drives yourself (tieing the appropriate lines to high), and that may not be an option for you.
Hope this helps-
Dustin W.