Lessee here...Does the number of practice rounds "really" make a difference for shot placement? It pretty much all goes south when the first incoming round shows up. Unless you practice with someone shooting at you.
Yes.
No.
Um... Right.
I would say it depends on your practice methods to some extent, but I think that if you are a good shot (which is based in part on how much/how well you practice), your shot placement will be better than otherwise.
Your skills will be degraded to some extent by high levels of stress. The key is whether you're degrading excellent skills (gained by extensive practice) or whether your degrading practically non-existent skills. How well you shoot in a high stress situation depends on how well you handle stress and how well you shoot unstressed. If you're REALLY bad at handling stress, you might be able to accurately say that "it all goes south" but in general, the better you shoot unstressed, the better you will shoot stressed.
The key isn't whether you're being shot at or not, it's whether you're under stress or not. There are ways to creat a high-stress environment without shooting at someone. This would allow them to learn to shoot under high stress and also to learn how to deal with high stress.