If Atheism is the rejection of all deities equally what is the polar opposite?
If an 'atheist' is someone that does not believe in all deities with equal disbelief, what would you call someone that believes in all deities equally?
Pantheism :
the worship of all gods of different creeds, cults, or peoples indifferently ; also : toleration of worship of all gods.
So you could say he is "pantheist."
'Theism', in it's broadest sense is the belief that at least one deity exists. From that, I'd say that 'Theist' may be the most obvious opposite to 'Atheist'.
http://www.merriam-webster.com/dictionary/theism