A Microsoft extension to the ANSI SQL language that includes procedural programming, local variables, and various support functions.
You would do this differently, if you were to move the business logic to a natively compiled procedure. You would not trap the concurrency error inside the Hekaton procedure, because the error can only occur on COMMIT (if I recall correctly). And in a natively compiled procedure, you cannot commit explicitly, as the transaction is the entire procedure.
So in a Hektaton procedure you would only have the UPDATE statements, and the loop with the trapping of the concurrency exceptions would be a in a regular T-SQL procedure that calls the natively compiled procedure in the loop, which means that you can keep the WAITFOR. from the page you linked to.