Yes, if a stored procedure contains a select which is the same as the one of a named query they will have the same execution plan.
But a stored procedure is more a kind of program, not just a select statement. You can write stored procedures with a lot of select statement, with one select statement or without any select.
Here you can find a short introduction to PL/SQL:
Using PL/SQL
Introduction to PL/SQL
Here is an example of a simple PL/SQL stored procedure that doesn't access any table:
Of course this doesn't make too much sense in real life.
John