Well - the rule-of-thumb is easy to remember: As far as Vienna Suite (Pro) is concerned, everything else than an EQ will lead to different results on a single channel, compared to the same plug-in using identical settings on a sub-mix of several sources.
From a technical point-of-view, VS Convolution Reverb would give you identical results, too, assuming that there are no individual pannings for any of the input sources (which is highly unlikely). In the same vein, VS Powerpan would give you identical results as long as you don't pan anything. ;-D
Every dynamics processor (i.e. VS Compressor, Limiter, Multiband), every modulating plug-in (in our case VS Hybrid Reverb), and of course every processor that uses any kind of saturation or distortion (e.g. VS Exciter) can't be replaced by an "overall" processor on a submix (with the possible exception of some academic examples with little or no practical use whatsoever).
Sidenote: As soon as you use EQs or filters _before_ their output is fed into a modulating and/or time-variant process on individual signals' channels, they can't be replaced by an "overall"-EQ or filter in a bus channel either, for obvious reasons. :-)
HTH,
