Domain Mapping and SEO

Looking for some advice about the use of Domain Mapping, Google Sitemaps and SEO.

I haven't yet used any of the SEO plugins or Sitemap plugin so I am flexible which way to go...

If someone has a site on my network and maps their domain to it, is there a way to ensure that Google indexes their content using their own (mapped) domain rather than mydomain.com/theirsite ?

Thanks.

Martin