I haven't rehydrated dry yeast since '96... have used SO4, S23 and Nottingham commercially without rehydration and saw zero difference in the finished product. I don't remember where the thread was, but someone had a vid up where they did a side-by-side comparison of dry yeast; rehydrated vs dry, and aerated vs non aerated. The progress of the fermentation was slightly different, but in the end they all ended up at the same place.
I put my yeast in the ferm prior to knockout... whether that means dumping int into a unitank in a brewery, or in the bottom of a bucket, and running the wort in after. My beers have an average lag time of about 6 hours from knockout to signs of active ferment. Works just fine for me... good starts, clean beer and one less possible source of infection.