Since the word "rock" appears in the title, presumably "rock-god" can only apply to practitioners of rock music. "Rock star" is the term you normally hear, however.
One could be a "god" of other types of music — country, classical, klezmer, what have you — but it just wouldn't be the same.
Still, the "almost deified by their fans" part is neither a rock nor even a recent phenomenon. It has applied to musicians throughout the ages. Frank Sinatra crooned to legions of screaming bobby soxers, Rudy Vallee before him became the first mass-media pop star, and way before that piano virtuoso Franz Liszt fornicated his way across Europe on the strength of his fame. From the Wikipedia article on Liszt:
After 1842 "Lisztomania" swept across Europe. The reception Liszt enjoyed as a result can only be described as hysterical. Women fought over his silk handkerchiefs and velvet gloves, which they ripped to shreds as souvenirs. Helping fuel this atmosphere was the artist's mesmeric personality and stage presence. Many witnesses later testified that Liszt's playing raised the mood of audiences to a level of mystical ecstasy.
Interestingly, a contemporary of Liszt, violin virtuoso Niccolo Paganini was so good that he was not deified, but said to have been possessed by the devil. I guess that's as good as music gets. Eat your heart out, Billie Joe Armstrong.