How difficult it will be will depend on how complex those interfaces are.
If the encoder interface is simple, for example a clock and data pin that returns only the position, then writing the code to talk to it will be pretty straight forward.
Some absolute encoders use very complex protocols. I can't tell you exactly how hard it will be because I don't know this encoder.
I would expect that writing the analog position feedback to the drive will be easier but I don't know exactly what the drive is expecting either. You wrote earlier that the drive manufacturer told you specifically that the drive would work with analog position feedback and no hall sensors. I don't see how that would de done from the datasheet. You need to be sure that this is true because otherwise this approach will be impossible.
You should start by tackling just the encoder half of the problem. Hook up the encoder to your DIO module and start trying to query it. I hope you have more information about its interface than what is found in the datasheet- otherwise you would either need to contact the manufacturer or do some experimentation.
Give it a try and if you run into specific obstacles then we can help you with those.
BTW- The easier solution is to throw money at the problem and buy motors, encoders, and drives that are compatible with each other. For example, NI sells motors and cRIO modules that can drive them, including brushless. At that point the software is just opening an example and adding your own position setpoints.
