One thing you should note is that a creature cannot use claws on the back limbs if they use those limbs to walk around, this is a limitation on a creature's natural attacks, as seen on this FAQ entry:
Claws and Talons: If I gain claw attacks, can I put those claw attacks on my feet?
If you are a bipedal creature (roughly humanoid-shaped, with two arms and two legs), your claws must go on your hands; you can not assign them to any other limb or body part.
If you are a quadruped (or have more than four legs), you can have claws on your feet. If you have claws on all of your feet, normally you can't use all of those claw attacks on your turn unless you have a special ability such as pounce or rake.
Talons are much like claws, but go on a creature's feet, usually a bipedal creature (especially a flying bipedal creature such as a giant eagle or harpy). An ability that grants you claw attacks cannot be used as if they were talon attacks (in other words, you can't "re-skin" the ability's game mechanics so you can use it on a different limb).
Example, a tiger (big cat) actually has four claws, but can only attack with two of them at once. The other two claws can only be used with the Rake ability. So, even if your GM does allow you to take extra claw attacks, the creature cannot use them (except for raking), unless he also creates a house-rule to ignore this limitation.
That said, looking at Evolve Companion we see that the possible evolutions are limited to the form of the animal:
Select a 1-point evolution other than pounce or reach from those available to a summoner’s eidolon. Your animal companion gains this evolution. The animal companion must conform to any limitations of the evolution. For instance, only an animal companion of an appropriate size and base form can have the mount evolution.
This means that you cannot take the Wing Buffet evolution if you do not have wings, or Tail Slap and Sting without having a tail, or, like the example given on the feat, be used as a Mount without being of the appropriate size and form (quadruped/serpentine) for that.
If the creature does not gain pounce or rend from another source, adding extra claws to her legs will not make any effect on her combat statistics. A wolf would benefit from claws on the front legs, for instance, but a tiger would not gain anything from adding extra claws to her feet.