Scalding hot water dissolves milk fats, so in general most nasties get washed away if you use scalding water immediately after feeding the lambs, and drain everything properly.
One of the things in my mind when we are advising a first timer bottle lamb rearer is that they probably will lose a lamb or several, and although one never gets blase, it is, for many people, just agonising the first few times. When it does happen, it is very reassuring for the distraught novice lamb-rearer if we can all say, "You really did do everything right, there is nothing here you can blame yourself for," and so on. So for that reason alone, I would always err on the side of caution when advising a novice. Plus, novices do make mistakes and not notice things a more experienced hand would spot, so the more things they do extra squeaky-clean right and which don't leave room for luck to be needed, the better their chances of getting some successful outcomes.