If brick units are placed dry on flashing, water is able to flow under the units rather than at specific points where weepholes are located. Will this flow of water contribute to freeze/thaw damage of the bottom brick units?
As long as water is leaving the wall, this should not be an issue. Freezing water can cause damage to the wall if it is trapped or confined. It is possible that a problem could develop in wall systems that are unable to weep because the base of the wall is clogged with mortar droppings. Even in these cases, the majority of problems that I have encountered are related to corrosion of steel elements rather than freeze/thaw heaving of the masonry. Laying units dry on flashing should not make them more susceptible to freeze-thaw deterioration. If anything, weepholes may increase the likelihood of problems because they increase the concentration of water, rather than if water can exit anywhere along the length of the flashing.