Oxford comma before "or"?
The comments so far haven't answered your question. There's quite an extensive explanation of the ins and outs of the Oxford or serial comma here.
You'll notice that the writer of the article says that "a serial comma or series comma (also called Oxford comma and Harvard comma) is a comma placed immediately before the coordinating conjunction (usually and, or, or nor) in a series of three or more terms."
So in answer to your question, the Oxford comma is not restricted to and.