I think we should slot White Night into this discussion.
In White Night, Harry uses Elaine's Name to connect with her, and then talk to her - but he only reinforced who she was, he did not somehow control her. Just not sure how to fit that in further.
As regards to conjuring by Harry, the biggest problem is the one Harry faces with the Erlking - containment. You can contain a summoned fairy, but humans have Free Will, and so can cross most circles. Add in his sheer bloody-mindedness, so even the common ways to prevent him crossing the circle (like, say, guarddogs, as used on Ivy) would not necessarily work - and once he's across your circles, you're in a fight for your life.