Austin, you are correct. The wobble is perpendicular to the bore axis. slightly more so on the right than left. Not sure where you were going with the trigger depression test, the firing pins do not rebound but the depression does lower the hammer, it does not change the wobblyness on either hammer when trigger is depressed. That said, when cocked, neither hammer has any appreciable wobble and I suspect that that is a good thing. I never would have thought to check this without your post.
Thanks

Hammer Wobble
 

Aaron: I read Don's post after I replied. I checked three more guns; a D lifter, a D hammer, and an A lifter. All of these had the 4 pin lock mechanism used on D grade and higher exposed hammer guns. All three had minimal side to side movement in the rebound notch.
I think the answer is that if your gun is a D,C,B, or A some lock work is in order; if it is a T,P, or G the lock is probably alright if it firmly engages the rebound and cocking notches.
I still learn something every day.

Best, Austin