Got this all working. This thread pointed me in the right direction. Meraki Collector for Sentinel : r/meraki (reddit.com)
I am using an Ubuntu VM, and apparently Ubuntu's implementation of rsyslog will, by default, only listen on sockets for log entries.
I had to enable UDP by uncommenting the following lines in /etc/rsyslog.conf:
module(load="imudp")
input(type="imudp" port="514")