Hi anthony02! I totally agree with your take on the use of the two Resin Systems; Acrylic being a water soluble resin (emusion) with the pigments ground into it, and Watercolour paints being bound usually by Gum Arabic, so they are two totally different systems.
However, I'm aware of several Profession Artists who state in published works, that they will use a little of either Acrylic White or Gouache for highlighted spots for "Sparkle", but we should remember that SAA produce a very fine Watercolour Opaque White for such purposes.
If more that "the odd spot" of Acrylic is used on a painting, then it should be classed as Mixed Media, and this would be an abiding rule anyway in competitions anyway.
I hope the above is clear enough, but come back to me if I can help any further.
Very best wishes,
PA & RSC Wigan / Warrington / St Helens