They each serve a different purpose. The Pro-Axle Guide makes sure the axle go in straight and the wheel is properly gapped. But if the axle slots are a bit crooked, then the axles will be installed a bit crooked.
The Pro-Body Tool will pilot drill the slots which generally straightens crooked slots. So if are not confident in the slots being accurate, the Pro-Body Tool would be important. You can then use the Pro-Axle Guide for insertion, but you could get by with just a gap gauge.