I currently have 235/80R17 on my dually can I go with a 245/75R17 on the back without them rubbing?

That might fit. The only way to be certain is to mount and fit.
What about the fronts? If the rolling diameter isn't identical, you'll confuse the Anitlock Braking System (ABS).
If your rig is 4WD, you'll also run into problems with that binding up.
I recommend matching all tires to be safe.