In theory the boat is sliding sideways leaving a slick to windward. That slick helps reduce the likelihood of getting over taken by a breaking wave but does not eliminate it. So, yes, there is a chance of a knockdown.
The reality is that there is no one right answer that fits all wind and wave situations and all types of boats. Heaving two is still a very valid way to ''park a boat'' in conditions where the wave height is less than twice the beam of the boat. (Current thinking is that it pretty much takes a wave more than twice the width of the boat to capsize a boat.) As wave heights get bigger other stategies such as towing warps or drougues may make better sense.