This is a two part question.
- Can summons benefit from magical healing?
- Can Eidolons benefit from magical healing? This question treats normal and unchained summoners as equal unless there is a specific difference where it concerns healing.
I have looked at the summon monster spell and it does not say that the monster summoned actually exists (for instance the eidolon specifically states that its an aspect of the creature and not the creature itself) or if its an aspect of a greater creature.
Reading cure light wounds it talks about what happens with living and undead, but nothing else is mentioned.