Is "Estimated Number of Rows" always per execution within SSMS execution plans?
Yes, this is the case - SSMS does not always show you the estimated rows * number of executions, and this can obviously lead to some inaccurate assumptions if you don't dig deeper as you did. But technically the answer to your question is no. Sometimes SSMS will get this estimate right, depending on the operator and other semantics.

In SentryOne Plan Explorer we try to compensate for this by showing SQL Server's rows * number of executions in several cases instead of just blindly copying the row count from the plan XML. Your plan, for example: