I've tried dry hops straight up and inside a bag with no difference that I noticed, they are just easier to clean out/remove when they are in a bag.
I always wash my yeast for later use, and I almost always use gelatin (unless it's a stout, hefe, etc). I have not seen any difference in the quality of my washed yeast whether or not gelatin was used. There very well could be something going on that I just don't know about, but the yeast still washes up easy and works well for me later.
