The simplest way would be for you to use the "Splunk App for Infrastructure" (https://splunkbase.splunk.com/app/3975/). However, on a Linux system, it makes use of both collectd and the UF, so if the requirement is that ONLY a UF is used, then the standard way of collecting data for SAI would not work for you. Before moving on to other options, I would point out, that installing and configuring collectd and the UF on systems is really simple, the app provides a simple script for you that does all the work for you.
Other options would be to use the *nix and the Windows Add-ons. They can be found here:
https://splunkbase.splunk.com/app/742/
https://splunkbase.splunk.com/app/833/
The Add-ons do not provide any visualisation of the network bandwidth data, and if that is what you are primarily interested in across both Windows and Linux system, you will need to create a dashboard showing the data you've collected.
