Rose, I wintersowed some hardy hibiscus in 2006. Germination rate wasn't great, but some did sprout. Two that I planted in full sun grew into nice healthy plants. Those planted in part sun didn't survive.
I know many people have trouble getting hibiscus to sprout. I didn't know that when I wintersowed them in my first year. I guess ignorance really is bliss. So if you have a lot of seeds, I'd sow heavily.
Karen