To answer your question directly, I'd recommend a gentle stir. It will introduce a bit of oxygen to your wort. Also, if you aren't pre-hydrating, stirring will help hydrate your yeast and get them active.
Yeast have 2 phases: aerobic and anaerobic. During the aerobic phase (while oxygen is present) yeast cells will consume the oxygen and multiply into more yeast cells. During anaerobic phase (no more oxygen), they are digesting sugars and making alcohol and CO2.
Not enough oxygen can lead to too few yeast cells. Too few yeast cells will cause a slow start where other anaerobic critters (bacteria, wild yeast) can get a foothold. You want to be sure your yeast are warm and ready and itching to ferment when you pitch!
An over abundance of oxygen, on the other hand, can lead to too many yeast cells. When the yeast are done, they will settle out and eventually start to break down. You also don't want to ever introduce oxygen to fermented beer, as this can lead to 'cardboard' off flavors. I wouldn't worry about over-oxygenating with a gentle stir.
Personally, I brew 10 gallon batches that I almost always kick off with a 1.5qt starter. I don't do any stirring; all the siphoning into 2 6gal carboys plus just dumping in the yeast, I believe, adds plenty of oxygen. But if I was sprinkling dry yeast on top, I'd want to give it the best shot to get a good strong start!