That's not how etymology is determined. The etymology of a word describes the reason why it's spelled or spoken the way it is. "Jizz" was chosen because it sounds like "jazz", but different. We can infer that the person who chose the word meant to convey that jizz music is like jazz music but different.

We can suppose that if the slang for sperm didn't exist that the writer would definitely have chosen "jezz", "juzz", or "jozz" instead, but personally I don't have any evidence to make that claim.