I happen to be a customer with both an LU300, LU600 or LU800 and a LiveU Solo - will my single login control both?

Currently, No.  Solo portal (https://solo.liveu.tv) and LU-Central, the management platform for LU300, LU600, LU800 and related devices, cannot share logins and you cannot use the same email address for both.  If you are a user of both platforms, you will need to use two different email addresses to access the management systems.