I'm looking to pull syslog data from my vSZ, APs and Cloudpath instance into a Splunk Cloud instance via http/https. Currently my vSZ and Cloudpath are hosted, one in AWS and the other by Ruckus, I have seen the Syslog options in both the vSZ and at the AP level to send data to a syslog server, which is not easily done with Splunk Cloud without hosting a Universal Forwarder out in the Cloud also.
looking at splunk cloud indeed it doesnt seem as you have many options. Are you doing any syslog collecting at all with Splunk? Unfortunately you can't install the splunk agent in the vSZ VM so indeed you will need a universal collector.
(unless maybe you can install the collector on a VM hosting some other application to which you get root level access).