Dry yeast does not require aeration because of the way it is grown; it already has a full supply of sterols, and aeration will not benefit it. When you harvest yeast, it is all the same no matter whether you started with a dry or liquid source. It's all liquid yeast now, so subsequent pitches need to be aerated. I have always used liquid cultures and repitched numerous generations, but am finding dry a more convenient first generation source, aside from the limited number of strains available: no starter, no rehydration, no aeration, just pitch. I haven't taken dry yeast out very many generations yet just because I'm trying different ones; but the manufacturers indicate that you can reuse dry yeast just as you would liquid yeast, and my experience seems to agree so far. Skipping rehydration of the first pitch should make no difference, AFAIK. If a few cells are killed, the remainder will grow to the maximum population your wort volume will support, and this is what you will harvest.