Again, I am just your ordinary Joe interested in sharpening, no authority or expert in the field, but this is what I have gathered by reading and by my own experience.
All of Spyderco's steels are premium grade and every single one can support an included angle of 30 deg. From my own experience and what I have read about what other people are doing to their knives, the top grade steels like VG10 and S30V can support even much smaller angles. But if I remember correctly there is also at least one Dragonfly in ATS-55 out there that is reprofiled to something like 15 deg INCLUDED angle...that would be Vampyrewolf's. But I have to correct myself a bit here. The steel is not necessarily the most important factor in the angle a steel can support. The hardness of the steel is a major factor and then again of course the use. A straight razor even though being made from a fairly soft steel will support a tiny included angle (< 10 deg, yes I mean included angle) in the application it was made for (shaving).
The main reason why Spyderco is sharpening at 15 (each side) deg and recommending resharpen at 20 is to save the ELU a lot of work. If they would sharpen at 20 and you would maintain your edge at 20 you would have to remove a lot more material because you are removing material from the entire edge bevel, while at an edge bevel of 15 degrees you resharpen at a microbevel which is only fractions of a millimeter wide and so 20 light strokes each side on the sharpmaker get the edge amazingly sharp. An added benefit is that for tougher cutting jobs, the 20 deg microbevel is a little more sturdy and resilient and will last longer, while it will take away very, very little of the cutting ability since that is mainly a function of the thickness of the blade behind the edge, which is still mostly a 15 deg. bevel. However, it is true that after many sharpenings at 20 degrees, the initial microbevel will become fairly wide and you have to remove more and more material with each sharpening and sharpening takes longer and longer. So Spyderco recommends to back bevel once in a while, which means that you are removing the shoulder between the 15 deg factory bevel and the 20 deg microbevel and restore the edge to a true 15 deg bevel again.
Having said all that, many, many knife afficinados that don't mind sharpening (like myself) don't want to sacrifice even the small loss in cutting ability associated with a larger included bevel and maintain their edges always at 15 deg per side, even if it takes a bit longer. Personally I sharpen always at 15 degrees and give it just a few strokes at the highest grit at a slightly elevated angle, about 17 deg. But I have read also about people how rebevel to 12 degrees and finish off with a few strokes at 15 deg per side.
Hope that clarifies things a bit. If you do a search for Jeff Clark and Joe Talmadge on bladeforums, you are bound to stumble across many very got thread on sharpening. The sharpmaker video is also excellent.