Thank you for the post.
Listed below are links to some documentation you may find helpful:
As long as you use the Filemaker Pro client, you shouldn't care about compatibility mode because the steps will be run by a filemaker client.
Filemaker server in the compability mode means supported in server side processsing. So inyour case you're fine beacuse you don't use server side scripts.
But let me use the occasion to point out that's it's very annoying that this ExecuteSQL is unsupported in server side scripst. That's teh huge omission that preclude the legitamate use of server side processing in many many case.
That's not to be confused with FMP 12's ExecuteSQL function, it's not the same goal the ExecuteSQL script steps is needed to target SQL sources outside filemaker. So you can't eplace it with the new function. So it needs to be supported by server side processing. FMS 12 was a huge disapointement in the lack of more server side supported scripts steps. I really hope FMS 13 will finally live up's the FMS9 marketing claim "ditch the FMB Bots"