Does Splunk Need an Agent?

A program like an agent is not required.

Splunk can read and index log data in any format without special adapters for IT data in various formats. Splunk can retrieve data remotely by reading files mirrored via syslog, SNMP, or rsync, or by reading files rotated on a central loghost via scp or ftp.

If your environment does not have a mechanism to collect data remotely, you can also use Splunk Universal Forwarder. Even in this case, there is no need to develop for the format.