Failsafes, mean for a robot point of view that it must come to a controlled stop when loss of radio signal is detected. This also applies to any weapons in that they must not activate unintentionally. It does not matter how you implement this as long as it works and can be demonstrated during tech check. From your point of view this could be demonstrated by unpluging the bluetooth adaptor from your laptop while driving/turning at full speed. If it then stops all is well.

I would also check that Bluetooth is allowed for remote control (though I cant see why it wouldn't be). I know that 433MHz tranceivers that are very cheap (<£10) seem a good idea but regulation don't allow for control but just telemetry of data as I looked at this a while back for another project.

I would still recommend you look at a Spectrum system, they are really not that expensive (dx5), espacally if you take into account of the 2 bluetooth modules and the joystick you need, unless you have a cheaper source than me.