Yep, that's it for the wholetone. As far as uses....it's most commonly used over Augmented triads, augmented dominant 7th chords, and dom. 7b5 chords. It'll pop up from time to time over altered dominant chords too, but that's not as common because it has a natural 9 and that note clashes just a bit. Because it's a 6 note scale and there are only 12 tones in western music, only 2 wholetone scales exist (enharmonically speaking) and they are a halfstep apart. So, you could just learn two fingerings for it and essentially know all you would ever need to know as far as they are concerned. Another thing...they are symmetrical scales, so they can be named from any note within the scale. In other words, using the one you wrote out as an example, that could be G wholetone, A wholetone, B wholetone, etc......just depends on what chord you're playing it over.
Yes, the 7th chord built on the 5th degree in the major scale is always dominant. In natural minor however, the 7th chord built on the 5th is a minor 7th, or if we're working in triads...just a minor triad. It doesn't sound that weird to our 21st century ears, but it was a bit different way back in the day. In harmonic minor the 7th scale degree is raised so that it is a half-step below tonic (thus becoming the leading tone). So when you build the V chord in harmonic minor, the third (which is normally minor) is now a major third. This is because a 3rd above the 5 scale degree is the 7th scale degree, which was raised when it was changed to harmonic minor. So now that the V chord is major, it has the leading tone so it has a much stronger pull towards the I chord and creates a stronger resolution. Also, in natural minor, the 7th scale degree is a whole-step below the the tonic (aka minor 7th) and the chord built on top of it is a major triad/dom. 7th chord. It doesn't have a very strong bull to tonic which, again, can be remedied be using harmonic minor. Raising the 7th degree also creates a diminished triad (or fully diminished 7th chord) a half-step below tonic which, again, creates a strong resolution.
The best way to understand all that is to hear it. Play the following chord sequences:
-Gm-Dm-Gm (natural minor....the V chord is minor and wont have as strong of a pull back to I)
-Gm-D (or D7)-Gm (harmonic minor....the V chord is now major and contains the leading tone (F#) and will want much more strongly to go back to I)
you probably get the idea for the next two....
-Gm-F-Gm
-Gm-F#dim-Gm
These are easiest to hear if you voice the chords so that the root and leading tone are the highest notes in the voicing(s)