I think that Brewer's Yeast you see in pharmacies and such is meant more as a digestive aid and such. I'd stick w/ baker's yeast for de-ox.
Did you notice less of a malt aroma when you were mashing? That's the biggest thing I noticed from the very start. My garage used to really smell like grain during the mash, but now, not at all. Supposedly that's because all those nuances from the grain aren't being oxidized. It's sure something I picked up on.
I wouldn't worry about the open transfer after the boil. As long as you're pitching active yeast right away, they'll eat up all that oxygen you added.