ORAC,
Granted, but how are you getting bearing discrimination? You'd need multiple receivers with a reasonable distance between them to get a decent number of cross fixes, i.e. a multi-static system the same as sites like flightradar use to track Mode C aircraft, except the receivers are also moving. So the problem then is you'd need to know the exact position of the cubestat and time of receiving a particular pulse from the transmitter. GPS might work for that if you've got access to receivers that work at orbital speeds* but I suspect if you've already got plans for a standard spy satellite it's just as easy to launch more of those?
Of course you can always just turn the radar off.
*COTS ones don't as I understand it.