Arnold used his own voice as the inner monologue of the hosts. Several times we see Dolores having conversations with Arnold in her mind. In S01E10 there's a log-in from Arnold's access code. These all may suggest that Arnold is living through the hosts' programming. In S01E10 Ford says: "Mozart, Beethoven, and Chopin never died. They simply became music."
And the last piece of evidence: At 01:19:57 Arnold asks Dolores "Whose voice you've been hearing all this time" where the voice of Arnold, Ford and Dolores merges. I believe Ford too incorporated his consciousness to the hosts' programming.
Are there other evidence supporting or against this theory?