Is it safe to replicate from a Solaris 10 ZFS v22 to a FreeBSD 8.3 ZFS v28?
Are there someone that have done this with specific versions of ZFS, where it worked perfectly?
There should be no issue sending a Solaris 10 ZFS v22 snapshot to a FreeBSD server supporting v28. Reciprocally, that saved snapshot, or any snapshot of a clone/descendant of the initial snapshot should be sent back to that Solaris box with no issue as long as you never upgrade the ZFS filesystem on the FreeBSD server.
What matters really are the zfs versions, not the OSes, given the fact the (Open)Solaris code base is used on both sides. Preserving upward compatibility for datasets (filesystems, volumes and snapshots) and pools is likely one of the rules that can't be broken by the ZFS developers.
Note: this somewhat happened in the past but ZFS was still beta: http://hub.opensolaris.org/bin/view/Community+Group+on/2008042301
Current zfs manual pages state about the zfs send stream:
In that direction, it should work. I don't know if it would work in reverse with the FreeBSD ZFS going to the older Solaris ZFS.