Hi,
"Does SSRS behave the same way?"
No, SSRS does not. SSRS use Http service. MSSQL Service might be unregistered in some specific case, but not "must".
The command syntax is like this string:
Setspn -a http/<computer-name>.<domain-name>:<port> <domain-user-account>
See http://msdn.microsoft.com/en-us/library/cc281382.aspx for more details about Register a Service Principal Name (SPN) for a Report Server.
thanks,
Jerry