Well I put 100 rounds of 115g blazer brass through my LC9. Was going to go for 150 rounds, but the range was prepping to close and I didn't want to waste ammo by hurrying through it.
All 100 rounds shot fine. There were no hiccups at all, despite the grooves on the hammer. An inspection check before and after shooting today showed that the grooves on the hammer did not get worse. It seems that the hammer can quickly wear in its first 100 rounds, but then it stabilizes. Primer strikes on spent rounds looks consistent.
I talked to the guys at the range about my problem, and they think the cause of different dent locations on the hammer is because the hammer drags itself across and under the firing pin on the LC9. So, when you put through a lot of rounds rapidly, the hammer will slide and bang around. Again, this is just theorycrafting as to why the dents are happening. Since the hammer is made of powedered metal, the divots could simple be metal compacting more densely, which would explain why the divots first form but then stop progressing.
So, I'm going to have to say the dents are non-issue. I'm not worried about them anymore, for now. I'm still going to get ahold of Ruger customer service and forward them my pictures just to see what they say. At the very least, it would be good to make them aware that this is an issue with the LC9, so perhaps they can avoid it in future models.
Can't say I'm not happy the LC9 is still performing though. I am going to keep checking the hammer every once in a while, but I need to stop letting it ruin the gun for me so I am going to put it in the back of my mind for now.