Native encryption is in Open-ZFS and Illumos since july together with SSD trim, special/dedup vdevs and sequential resilvering. While I have added support into napp-it, I hesitated to use the new features in a production setup as they are all ultra critical. Always good to wait some months as the early adopters are the first to find bugs.
In the meantime, there were some bugs found like a corrupt pool when adding/removing special vdevs with different ashift, corrupt pool when enabling trim on certain SSDs, panic when importing a pool with the large dnode feature enabled to name the most important - although they are all very rare and most are not affected. All these bugs are fixed in the meantime or a bugfix is under way, see Issues - illumos or join the maillists from OmniOS/OpenIndiana/Illumos or ZoL.
In the light of this, it is a good sign if you do not find remarks for encryption on OpenIndiana (or OmniOS, SmartOS as they use the same Illumos as source). It shows that encryption just works without conspicuousness.