What the actuator is going to do isn't really important, but in this case it will let a shovelblade up and down
I see a couple of possibilities:
1) If the dozer is always in view of the operator, then the Arduino isn't really needed: The actuator should have its own built-in limit switches (check on this first, though), and you only need to switch the polarity of the motor (in whatever manner the actuator needs) to change the direction of travel. The operator can see where the blade is, etc. Then, all you need is a way to switch the direction of the motor with the R/C controls. There do exist boards for the R/C crowd that allow you to switch relays or such using your transmitter (they are commonly used for auxiliary items in R/C). Or, you could use a small R/C servo to switch a couple of regular switches mechanically.
2) If you really wanted to use the Arduino - then you could use it to decipher the servo signal stream output by the R/C receiver for the channel for blade control, and convert that PPM signal into something to tell the Arduino to output on a couple of digital pins LOW-LOW (no movement), HIGH-LOW (movement in one direction) and LOW-HIGH (movement in the other). This is kinda what your diagram seems to indicate (so you seem to understand that much). This is essentially what the first option above does, though (though it may not necessarily use a microcontroller to do it - it is possible to do the whole thing without needing a microcontroller).
For bonus points, if the actuator has a position output sensor (potentiometer or pulse counter), you could read that to determine a stopping point based on its output (in the case of a pulse sensor, you would have to set things up to allow the position of the actuator to "hit the stops", so you could hit a stop, then reverse direction to count the number of pulses to the other stop as a calibration procedure on power-up, so the Arduino can know, based on pulse counts, where the blade is positioned).
Now - if the dozer is out-of-sight, remotely operated with a camera/light system on-board (?) - having the Arduino be able to read the position could be helpful in that you could send that telemetry back to the control station, and use it for some kind of indicator to show the blade height for the machine (since is may not be able to be seen directly).