One thing we have to remember is that Hubpages is already serving up a site map to search engines. Several, in fact. You can browse them yourself by following the addresses at the top of its robots.txt file:
I have yet to see any evidence that cobbling together our own sitemap and submitting it manually will have any positive effect, since we'd simply be trying to duplicate what Hubpages does automatically.
It doesn't make sense to me. It's like calling up the phone company and telling them your phone number, when it's already listed in their directory. Would that really result in your getting more phone calls?
I could be wrong, but if so, I'd like to see a study showing for certain that duplicate sitemaps generate more traffic than just one sitemap. (This is a little hard to do, unfortunately, since it's hard to isolate just one factor, like a sitemap, ruling out any other factors that might be causing traffic fluctuations.)
The "submit a sitemap" advice is really for people with their own websites, which will NOT have sitemap unless they create it themselves. There are a lot of extra things you have to do when you build your own website. The advantage of publishing on third party platforms like HP is that they've done a lot of that setup for us. ;)