To find the actual account names, press Windows+x and then select "Computer Management". In the MMC, under System Tools, expand "Local Users and Groups", and then click on "Users" - you'll see all the actual accounts in there:
Mostly these will be the first names you've specified on the Online accounts, but in some cases they may be padded: for example, one of the accounts appears to be:
I believe the core of the account linking is actually handled by the Windows Home Server Console app that can be installed on Windows 7 and lower - I've not yet installed 8 properly, only Windows RT.
The WHS Console would automatically configure a number of shared folders for the accounts that are configured on the local machine when it is installed, and presumably would add your local credentials to the Credential Manager but for the WHS name thus allowing "seamless" interaction with the server over the workgroup - which is really just a way of grouping an otherwise disparate, unconnected set of machines.