Only play a G minor pentatonic over and entire G minor chord progression?? Although it would work, wouldn't you get tired of only using a single 5 note scale over an entire chord progression?? If it's your thing thats cool, but honestly I find it very and alittle too limiting to the range of harmonies you can play (some chords may have to be broken down to only 3 or 4 harmonic intervals). And you would often find what you would put to it to be very weak and boring.

Layering the pents is cool to form a sort a jointed scale of pents. I tend to layer the two blues scales together, which forms the same scale but with an added (b5). A Nice addition.

For single chord harmonization: The (b5) works as a lydian tone over a major chord and the blues note over a minor chord. The (b3) works natural with a minor chord, and gives a bluesy type sound over a major chord. You often have to exclude the natural 3rd when playing over a minor chord, due to it's unsettling clash with the minor chord's 3rd. Since the scale is made up of both (b3, and b5), it also works relatively good over a diminished chord. Although the 6th in the scale is the same as the diminshed 7th's (bb7), it's context in the scale may cause incompatibility. Most likely another scale would work alot better.

As for harmonic generalization: It is not as compatiable because many tones will be excluded because of clashing of intervals of a given chord progression. You are often only left with 3-4 good notes per chord, which to me is unacceptable. I'm picky I know. :p

Also, I'd like to correct something I wrote in the previous post about the harmonic generalization of modes. Modes can be used as a generalized scale over a chord progression if that chord progression is in that mode. You should look for it to be either major or minor first. Mostly likely that is going to be the correct way to look at it.