OK, here is my revised unchained summoner.
The role he would take is rogue/scout, with his eidolon serving as adviser and skill helper, but disappearing during combat. He'll have some face abilities, but more as a secondary one as he will lack the skill points to focus on that as well.
His motivation to accept Iliara's invitation is basically infiltrating the Hellknight-held area, instinctively hating them due to their origins in Cheliax but knowing himself too weak to fight them directly.