Yes, there will surely be some wear with a new or rebuilt manual tranny. But, when you consider the use of break in dino oil for a transmission, I'm not convinced. I can understand changing and inspecting tranny oil at 100 hours or so, but a tranny's moving parts get a free ride when compared to the temps, pressures, and speed of ring/cylinder wall contact. Dino oil, then synthetic for a lower end engine rebuild makes sense to me, but not for a tranny.
Of course, there are some long-held beliefs that younger mechanics delight in trashing. Many young engine builders say the time-tested means of breaking in a new/rebuilt engine, i.e., dino oil, vary the rpm's, don't go over 4,000, change oil at 50, 100, 300 miles or some variant, then only synth after break in, are outdated. New machining techniques for cross-hatching cylinder walls and better metallurgy on rings mean that you should break in a new engine fast. Don't baby it, smokehole it! Some tuners even say a dyno break in for a new Subi engine is the way to go. A couple hours on a dyno, and you're good to go.
Of course, as we know, car guys can't agree on what day it is.
Subaru manuals are silent about tranny break in. Even for a new engine, they only say to keep it under 4000 and change oil at 1500 miles. Nothing further needed.