Domain Mapping in Multisite

[ScotPress]

Scenario...

One main site, ie mine with a large number of sub domains ie Joe's Butchers and Nellie's Hair Salon

Am I correct in thinking that if I was to manage a sub domain for joe's butchers on my main website that if I domain map it to his url joesbutchers.com for example it would look like he had his own website on his url?

If so how does the SEO work? Does the seo map to his site or stick to the sub domain? Just keen to know if someone searches for Joe's Butchers what site they'd find - mine or his domain mapped url?

Or am I just being well stupid and got that wrong.

Just thinking along the lines of how wordpress.com works and trying to do similar for a whole load of small businesses.

Keen to run it on Synthesis & Genesis Prose.

If this is feasible is it still possible to add Genesis Connect and BuddyPress to it as well?

An ambitious project but champing at the bit to give it a try...