From Splunk Wiki
As of version 4.x, Splunk is officially supported on FreeBSD 6.1 and 6.2 (x86). To run Splunk on 32-bit FreeBSD 4.x, install the compat6x libraries. Splunk Support will supply "best effort" support for users running on FreeBSD 7.x.
To get the libraries, run:
Running Splunk on FreeBSD 7.x is often discussed on the Splunk forums.