Not sure why there would be an increased infection risk, and I am using similar process to you (with aerating plastic tip at the bottom of the transfer tube) but I think we are still under-oxygenating the wort by quite a bit. That's bigger downside than any risk of infection from getting oxygen from air in.
Is the goal oxygenating or aerating?
I'm not specifically infusing my wort with pure oxygen but i am creating a situation where all of the liquid had an opportunity to make contact with the air and slosh around (aerate). By having the impact point of my stream be the side of the bucket, the surface area is huge... It's got to be more effective than a vigorous stir?