Hello Adam - I believe it can.
If you take a look here:
https://www.ibm.com/support/knowledgecenter/en/SSEPCD_10.5.0/com.ibm.ondemand.ir.doc/dodiz058.htmThat's the doc for the OS/390 Indexer on Multiplatforms.
The OS/390 Indexer is now common code between all platforms, and I also believe it's written in C.
Anyway, in the doc for multiplatforms you can see all of the exits listed as available.
On z/OS there is a sample ANYEXIT in C in SARSINST(ARSECANY).
/*********************************************************************/
/* */
/* MODULE NAME: ARSECANY.C */
/* */
/* */
/* SYNOPSIS: OnDemand 390 indexer sample anystore exit */
/* */
/* */
/* DESCRIPTION: This module contains the ANYEXIT function */I, personally, have never done any exit work for indexers so I'm afraid I can't be of much more assistance.
Ed