If I use several master pages for different online header/footer navigation block groupings, assigned to a WebHelp target, is the Online condition tag unnecessary for those navigation blocks? That seems logical, but what do I know?
Well, a simple answer would be to generate your target without excluding the online condition tag and see if they appear.
Basically, you're asking whether your output uses a master page or not; so that depends on:
a) Does your target actually support master pages? Word and FrameMaker do, but PDF does not.
b) If the target supports master pages, how do you apply the master pages? i.e. using the target setting, and/or using styles (html classes).