Multiple Service Accounts

Just wondering what happens when you add multiple service accounts to an SE account.

Does it definitely definitely allow concurrent login to each account (my assumed answer) or from SE's perspective is it just a means to extend beyond the 8 character limit on a normal service account, but doesn't allow dual boxing?

EDIT: For reference for anyone else worried about this, I took the plunge and it does work. The account selection page appears after you click the play button over the top of the character selection, then you can choose which service account to use.