From my experience most DTrace users rely on DTrace "providers" [1] and Static Trace Points [2] rather than directly probing kernel structs. Also these days the Solaris kernel is not moving all that much.
DTrace isn't limited to Solaris. Per Wikipedia, it's in FreeBSD, NetBSD, Mac OS (but you can't use it with SIP), and Windows. And lots of userland stuff too.
[1] https://www.illumos.org/books/dtrace/chp-syscall.html#chp-sy... [2] https://www.illumos.org/books/dtrace/chp-sdt.html#chp-sdt