Osmotic pressure only exists across a semi-permeable membrane, so RO water does not have more osmotic pressure than any other water. It is water. Osmotic pressure is better understood as the tendency of water to move across the membrane in order to balance both sides. When there is something that can NOT move through on only one side of the membrane and not on the other it creates physical water pressure on the membrane from things like water that CAN move across the membrane - water will do so until the pressure on both sides of the membrane is in equilibrium. In reverse osmosis, pressure is added to one side to force the water across the semi-permeable membrane, leaving the other stuff behind. I'm sure you can google much better explanations.
Yeast in RO water experience higher osmotic pressure than non-RO water, but not higher than distilled water. Adding extract to the water before adding yeast will relieve the osmotic pressure.
And while there is some osmotic pressure created by using distilled water, it is the best media for long term storage of yeast.
Started this post before all of these other replies. Bah.