Ok I am sure I might get railed by these questions but here goes-
1. on a single speed is the rear wheel is the same as a normal 12 speed ( just that it has one cog on it - so same size hub )does that question make sense?
2. and are single speeds free wheel or not?
1. You can use the same size hub with a SS freewheel, but you may have to re-dish the rim (pull the rim off-center using spoke tension) and use a spacer on one side of the hub in order to get the rear cog to line up with the front. Some hubs are made for SS and are made to align properly without any spacing issues.
2. Singlespeed generally implies freewheel. If someone is talking about fixed-gear in particular, they will usually specify.