Looks like Toad does not play well procedure return values. What if you turned it into a select query in an Execute Script step followed by a set variable value step?
Select Contact_Feed.Load_Vcast_Accts_To_Contact(Out_Success) TestResult From Dual
name the result set variable say ResultSetVar
Then in the set variable value step set the variable value for Load_Success to #ResultSetVar.TestResult#
Just an idea.