I would think it should be fine. Just pull the red wire on the RSPro and use the Rx pack. The BEC wount hold up to 4s. Watch your gearing to start with untill you get a feel for motor and esc temps.
I've run a R1Pro for long time in a 1/8 scale buggy and had great sucess with it so I would imagine that the sensored version should be fine as well. I know the R1 and RS are basically the same thing except for the sensor wire port. In all honestyyou probably dont even need to use the sensor wires, it should run just fine in sensorless mode.
I can't decide if its more fun
to make it...
or break it...
since everyone seems to have an "good" esc at the LHS, how would an RSpro fair with a tekin truggy 2250 motor in an e-maxx? with the usual bec/caps/fan...