I think I'd prefer "reactive" to "retaliatory." Sure, it's possible for someone to manually snipe in 5 seconds or less. I've done it, but that was when I had a cable modem and even then I was bidding "blind," without regard to any last-second bids that had been placed.
I'd like to know more about "snipe nibblers" too. Don't think I've ever run across one of those.