Yes, yeast require O2 through the growth phase
Actually, dry yeast needs nowhere near as much dissolved O2
as liquid yeast. The reason being is that dry yeast is propagated aerobically in a bioreactor. Propagation in bioreactor allows the glucose content in the medium to be held in a steady state below the Crabtree threshold of 0.3% glucose weigh by volume. The result is that all growth is via the respirative metabolic pathway. Propagation via the respirative metabolic pathway results in yeast cells with fully charged ergosterol and unsaturated fatty acid (UFA) reserves (it is also over an order of magnitude more efficient).
All reproduction in batch-based liquid yeast propagation and beer fermentation is fermentative because the glucose level is above the Crabtree threshold. What yeast cells do when O2
is available is shunt it along with a small amount of carbon (sugar is carbon bound to water) to the respirative metabolic pathway for the production of ergosterol and UFAs.
With a batch propagated liquid culture, initial O2
demands are based the point in the process where the cells are harvested. Pitching a culture when it reaches high krausen places a lower O2
load on the wort because the cells still have ergosterol and UFA reserves. Waiting until a culture reaches quiescence (i.e., waiting until it ferments out), increases initial O2
requirements because the mother cells that were alive while O2
was still in solution share their ergosterol and UFA reserves with all of their daughter cells. Allowing culture to proceed beyond high krausen results unnecessary ergosterol and UFA depletion. Reproduction after the end of the exponential phase is for replacement only.