While you can tune a load to the rifle without the barrel tuner (is this a Browning BOSS or similar device?), it will cause you to be limited to certain velocities that result from the bullet and powder charge combinations that work without the tuner. The whole point of the tuner is to let you tune in whatever load you choose to shoot and not be married to those particular combinations. So my approach would be to set the tuner on its mid-range adjustment point or, in the case of the BOSS, the middle of the range they recommend for my bullet weight, then work up the load to the pressure and velocity range I was comfortable with for whatever shooting purpose I had in mind. Then I would finally adjust the tuner to further minimize group size.
If you want to try tuning a load first, then bringing the tuner into play to see if it can improve the result further, that's a perfectly good experiment, but in theory, it shouldn't be necessary. I'm inclined to think the tuner changes the dynamics enough that there may be an advantage in having it there during the initial workup. Once you have the loads tuned as best you can, then try messing with other precision loading techniques to eliminate bullet runout, case runout, more careful primer seating, case preparation steps and such to see if groups get still tighter.
