According to the manual for the"MyRIO" found at this link: http://www.ni.com/pdf/manuals/376047a.pdf
There are two blocks of 8 bit DIO for the MXP ports and one byte available on the MSP port. The issue that might exist is the voltage output level is 3.3 volts. The other thing that I don’t care for with a lot of National Instruments DAQ style boards that are the cheaper ones … they can’t drive anything worth a crap off of the ports. The good thing is the ESC’s can accept 3.3V signals and it is at least worth a try. Worse case scenario would be to have to put a line driver buffer in line with the signal to make sure it can supply enough rear to do the job.
From what I can tell in the documentation you have three PWM lines between the MXP ports and two on the MSP port. The one thing I see is the PWM lines between the two different ports have the same name … so I get the feeling it is only assigned to the secondary I/O function of a PWM port once for each signal name.
You should be able to setup a timer routine to use a regular DIO line to toggle on and off to create a PWM signal … considering how slow of an update rate you are dealing with. The “speed” control would basically feed the timer which is going to toggle the signal. Pretty simple to do.
The other thing is … this unit has an FPGA that is doing the I/O so I am not sure exactly how the software will function with this. From the little bit that I have been readings on ni.com … this thing is a school based learning system and frankly not much more than a fancy toy. Life would be better with a real DAQ and using LabVIEW to run your code.