Dave,
I got red bugs in my system twice...now every new coral gets dipped in interceptor before getting put in the tank.
Red bugs are livebearers,(meaning no eggs) and they do swim, fast. However, they cannot live longer than a week without acros to eat, and they are acro specific, no acros = starvation.
With all that in mind, I personally would feel comfortable in your sytem with dosing both of your display tanks only, not the fuge, (it doesnt have any acros as I recall. If it does..pull them and place them in a display). Any that escape the treatment wont survive long without the acros to eat.
I say this because with your system designed the way it is, I honestly dont think that any redbugs could make the journey from your sump back into a display. In fact, I'd be willing to bet that you only have them in the cube, and not the long display. If you've got them in the long display, I'd bet money you transferred them to it from the cube via frags.
I only needed to do two treatments for redbugs and that wiped em all out of my system...It wont hurt to do a full three treatments to get them from your tanks though...
Nick