As is common with these types of threads, definitions are vital. If we're using the same terminology to imply slightly different meanings, then the arguments are completely lost.
I take sideslip to mean an angle in the horizontal plane between the longitudinal axis and the flight path relative to the air.
If I'm flying a twin with the left engine out then in the normal rudder position, there will be dynamic pressure on the right side of the fuselage. If I have enough right rudder to stabilize at a point where there is even a small amount of dynamic pressure on the left side of the fuselage, then the obvious continuity of this process would imply that there is a rudder position in between where there is no dynamic pressure on either side of the fuselage. That point meets my definition of zero sideslip.
That point would probably be a minimum for profile drag, but if it takes a significant amount of rudder, then I'd be surprised if it were also a minimum for total drag.
Matthew.