The Spike can be used to control certain motors if you don't need throttle, just on/off, although per table 4-4 in the rules, you can only legally control 1 motor with 1 spike, in which case you wire M+ to the motor's positive and M- to the motor's negative.
WITH THAT SAID
Outside of the competition, you can in fact control two motors separately with a Spike. Wire one to the M+ and another ground somewhere, and the other to M- and some other ground.
SEE:
http://content.vexrobotics.com/docs/...uide-sep05.pdf
EDIT: @cpapplefamily: A regular motor controller can support 2x of the motors that a Spike can support 1x of. You can never have 2x motors on a Spike. Additionally, a CIM is not one of the motors listed as being able to run 2x of on a proper motor controller. Furthermore, you would never want to, because that one motor controller is still limited to the same 40A breaker, which 2 CIMs could pop in a heartbeat.
What CAN be done, which I believe your mentor may have confused with what you wrote, is that you can have 2 motor controllers on one PWM signal, using a Y cable and 1 PWM port on the RoboRIO.