I am not sending any additional/custom attributes through to Accelops. I believe they are only looking at the nameid in the subject of the assertion.
To change this value you would modify the application uesrname format from the Application->Sign On->Settings menu.
I haven't seen the latest AO SAML documentation but that is how i have mine configured and it works fine. If you are trying to populate additional information for users in AO i don't know if their ACS does that, we use LDAP to populate the users but SAML for authentication.