Well, it outright says
"Eidolons can select any feat that they qualify for, but they must possess the appropriate appendages to use some feats. Eidolon feats are set once chosen, even if the creature changes when the summoner gains a new level. If, due to changes, the eidolon no longer qualifies for a feat, the feat has no effect until the eidolon once again qualifies for the feat."
So, if you took simple weapons as an evolution, you would then qualify for Martial weapons as a feat.
Now, the other way around... that COULD be seen as not allowed, although I think most GMs would allow it, simply on a which came first the chicken or the egg? idea in that it's 2pts OR a feat for each level of weapon proficiency... So to say you can't spend 2pts for the evolution of Martial because you took simple as a feat first... seems kinda overly critical to me.
It would have been better if they had said "If the ediolon already has simple weapons, then it can learn martial for 2 pts" or something like that but, like I said, to me it's really a chicken/egg question.
Speaking of egg-laying birds, I'll leave you with a quote from Sean K. Reynolds that fits here I think about how things that work exactly the same way but aren't called such exactly are still the same.
If it walks like a duck and quacks like a duck, it's probably a duck. If you line up Daffy Duck, Donald Duck, Duckman, and Howard the Duck, from a game standpoint it makes sense that a +1 duck-bane arrow is going to do +2d6 damage in addition to normal arrow damage if you shoot any of them, because they're all ducks. And if you shot that arrow at "Duckie" from Pretty in Pink, it wouldn't get any bonus damage, because he isn't a duck. And you should be able to see why those first four are ducks and the last one isn't.
I went and checked because the way both of you commented on the issue it seemed like you think martial proficiency has simple weapon proficiency as a prerequisite. But it doesn't.
So if you intend on using a martial/exotic weapon with the Eidolon, no need to pick simple weapons proficiency feat first, nor select the evolution granting it.
As for the scenario involving the evolution for martial weapons based on a simple weapons proficiency feat, like AbsolutGrndZero i'd say you can skip the first 2pt evolution cost for simple weapons.
It has its use. Being proficient with all martial weapons versus a single type. But it costs 2 evo pts more down the line. At some point you can fall back to simple weapons to and save those 2 evo pts too.
Jelly