Hard to say odds on seedlings, exactly Keith. Even if it does self-pollinate it still could produce plain seedlings. It could also be getting pollinated by another plant across the street. You just can't know unless you have it indoors and isolated. Sow the seeds, one to a cell and see what you get. You'll probably get some variegated babies and you can just give or throw away the others if you don't like them.
But I can tell you that if you really want to propagate it, the odds are very good you'll get variegated plants if you start from cuttings.
I'd recommend you wander over to the Hibiscus forum for advice on starting Rose of Sharon from cuttings because I'm not sure what time of year you would want to start them. I've only done tropical varieties of Hibiscus that grow year round.
