I'd love to hear someone from Meraki explain the rational behind this limitation, if any.
FYI, there are plenty of legitimate reasons for a log management service provider to use FQDN vs. IP (load balancing, fail-over, etc.)
"The important thing about DNS is that it provides more than just A records (hostname = IP). DNS provides different types of records such as MX, CNAME, TXT, etc... that may be required by some software, sometimes. It allows multiple address records, IPv4 + IPv6 records, dynamic addresses, load balancing, geo location based resolution, fail-over/redundancy, etc... DNS tells you what things are (www.google.com is google's web service, 172.217.4.110? What's that?) It allows you to change these settings/records and have them picked up by clients without making changes on all the clients. DNS can do complex things.
There's often a clear advantage to using DNS over a direct IP address.
FQDNs can be a requirement
Some things like web servers that use name based virtual hosting or load balancers, etc... absolutely require that you address them via an FQDN or hostname. They determine how to respond to your request based on the FQDN that you are connecting to. Connecting via an IP may not work at all.
SSL certificates are issued based on domain names, so you may not be able to use some SSL enabled services (properly) without DNS."
https://serverfault.com/questions/788862/why-should-i-use-an-fqdn-instead-of-the-servers-ip-address