Best way to send a simple digital signal wirelessly (close-range)?
Yes those RFM12BSP transceiver boards will work, but you will need a microcontroller on both sides of the link to send/receive the data from the transceivers SPI interface.

If there will always be an unobstructed line of sight between the device and motors, then it should be possible to construct something using infrared akin to a TV remote, with an IR Emitting diode and an IR receiver such as the TSOP4438. You will need to drive a 38kHz signal in to the LED from a microcontroller such as an arduino. The presence or absence of the 38kHz clock would produce a logic high/low on the motor side. The benefit to this would be a far simpler circuit on the motor side.