Switch for SMC CXS

Can a D-M9 Series auto switch be used on SMC actuator CXSWM25-100

No - it's not possible to use D-M9 switches on CXSWM  with -or-  without a bracket (adapter sleeve).
The following switch Series can be used: Y5, Y6, Y7, Z7, and Z8.
See page 782, datasheet https://content2.smcetech.com/pdf/CXS.pdf