We are getting ready to conduct a PoC on Splunk SaaS solution and for that, we have some challenges in opening firewall ports for each test machine. Is there any way to configure a single Splunk forwarder with access to Splunk SaaS and then the on-prem servers communicate with the forwarder. This way there is only one outbound connection.
Since it's for a POC I'm going to guess that the amount of data you're sending isn't terribly high volume. You typically would want multiple intermediate forwarders in a production environment for high availability and load balancing. For the purposes of a POC you'll probably be fine with a single forwarder.
Make sure you install the forwarder package that is provided by the Splunk Cloud team that has all the correct certificates to communicate with your Splunk Cloud instance on the intermediate forwarder.