As most aliases on the Control Console are also aliases of accounts on the mail server and route to the same mailbox, this has not been a common issue. A better setup for the organization would be to set the alias accounts as primary accounts, and configure alternative delivery destinations for the Spam Report, thus keeping the delivery destination the intended account while still allowing the Customer Administrator to receive notification of quarantined spam.
This can be done once the user account is configured as a primary, under the Email Protection tab within the user details. You may need to configure the ability to set the alternative delivery destination under Email Protection > Policies, and editing the policy applicable to the user account. The setting is within the policy under Spam > Reporting.