If you've ever kept red plants like Ludwigia 'Red' in lower light levels, you'll quickly see it revert to green coloration...it stays quite happy and healthy, it just isn't that lovely red color we desire. This is because many plants produce their red pigments when they're receiving too much light; essentially, if you overdrive the chloroplasts, they're producing an equivalent of sunscreen to block excess light. So some red plants are trying to block most light, not simply red.
As far as greens being useful for photosynthesis, they are useful but they're not as useful as certain other parts of the spectrum. The main reason we run two greens (a 525nm and a cyan 505nm) is because it separates out the shades of greens and renders those colors extremely nicely. In fact this was the first thing I ever noticed about the Dutch 6300K spectrum when I placed it on one of my tanks...my wall of lime green plants were no longer all the same color and I could now see darker olive greens, light celadon greens, deeper emerald tones, and so on. So while all the red LEDs in this spectrum make your red/pink/orange colors really glow, don't underestimate how it enhances greens as well.
I hope this answered or clarified your questions, but if not just let me know!