I've tested this call against several filesystems on cDOT OnTAP 9.6P2 volumes using SDK 9.5, 9.6 and 9.7 since I still had all 3 "laying around". By default we use 9.7.
The acl-type field returned for previous OnTAP and SDK versions used to return the ACL type of each file and directory encountered, almost always returning "nt_acl" or "nfs_acl". It now returns "unknown" for all objects.
I haven't used the call for some time, and I'd have a pretty hard time determining the version of either that actually worked. Sory about that, I wish that I had more detail on when it broke. I suspect that the issue is with OnTAP, not with the SDK.