I have been to link provided in your mail. But it just say "The stored procedure can be written in any language supported on that server, except for REXX on AIX® systems. (Client applications may be written in REXX on AIX systems, but, as with other languages, they cannot call a stored procedure written in REXX on AIX.)" and nothing on REXX Exec to call SP.
Go thorugh the above links and then in the REXX REFERENCE manual, Chapter 8.6, 'Summary of Writing Execs for Different Address Spaces',
there is a summary table listing the the REXX keyword instructions, built- in functions, TSO/E external functions, TSO/E REXX commands and other services you can use for execs that run in TSO/E and non-TSO/E address spaces.
You need to spend some of your time on these - I don't have something ready-made at this moment...