fstyp(8) should have the ability to detect ZFS pools. It should be possible to detect them by using the same algorithm as the dump_label function from cddl/contrib/opensolaris/cmd/zdb/zdb.c
This is being worked on (actually looks pretty much ready) at https://reviews.freebsd.org/D2045
A commit references this bug: Author: allanjude Date: Fri Jun 19 05:09:05 UTC 2015 New revision: 284589 URL: https://svnweb.freebsd.org/changeset/base/284589 Log: Add the ability to detect ZFS and GELI encrypted file systems to fstyp(8) Functionality is hidden behind the -u flag to avoid confusing automounters PR: 200823 Reviewed by: asomers, eadler, wblock (man page) Approved by: trasz MFC after: 10 days Relnotes: yes Sponsored by: ScaleEngine Inc. Differential Revision: https://reviews.freebsd.org/D2045 Changes: head/usr.sbin/fstyp/Makefile head/usr.sbin/fstyp/fstyp.8 head/usr.sbin/fstyp/fstyp.c head/usr.sbin/fstyp/fstyp.h head/usr.sbin/fstyp/geli.c head/usr.sbin/fstyp/zfs.c
A commit references this bug: Author: asomers Date: Thu Feb 15 00:11:43 UTC 2018 New revision: 329288 URL: https://svnweb.freebsd.org/changeset/base/329288 Log: Fix utils_test_007_pos The test fails due to an fstyp(8) usage difference between Illumos and FreeBSD. Fix the usage. PR: 200823 Sponsored by: Spectra Logic Corp Changes: projects/zfsd/head/tests/sys/cddl/zfs/tests/utils_test/utils_test_007_pos.ksh
Sorry, I wasn't even aware of the IllumOS version when I wrote the FreeBSD support from scratch on an Airplane on the way to some conference or other.