the vCloud Application connects to the Oracle DB as the user vcloud.
So if you login as sysdba, you'd have to connect as vcloud. however, you don't have the password since it's random and encrypted.
What you might be able to do as sysdba is see if vcloud account is locked or if the password expired.
As a side note/reminder, the appliance is only for Proof of concept and not production purposes. there is no migration method to go from the Appliance to a full instance either, so just be aware of that.