I have splunk-5.0.2-149561-freebsd-7.3-amd64.tgz running on v9.1
I found that just installing the FreeBSD 7 version will work just find on v9.1
Splunk 5.0.1 only has FreeBSD 7 and 8 as supported operating systems. See the System requirements topic in the Installation Manual.
None that I have heard announced.
Any plans on when it will support v9+?