Please check out this post on Splunking data from a Raspberry Pi. That post seems a bit more oriented toward Splunking the Pi itself, but parts of it are still very useful.
If you are using the Pi to read data from a serial port, and you can write that data to disk, then the Pi side of Splunk just got way easier. Follow the first step from the above link to install Splunk if required and set it up to receive. Then install the UF as per step two.
For step three, you probably won't need the scripted input. Instead, set up a monitor stanza in the appropriate folder (probably something like /opt/splunkuniversalforwarder/etc/system/local/inputs.conf) on the UF on the Pi to read that file. I think the second example here may be about all you need. Continue with the last sub-step of step 3 - setting up your outputs.conf.
That should be it. You'll have to work the Raspberry Pi end of things a bit to get it to read from serial and write to a file, but the actual bits of python don't seem too hard according to here.
