I have the same experience as @BlakeRichardson. I'm on the IT vlan and I have cameras on a variety of other vlans. I didn't have to set up anything special to get direct stream working. My vlan has access to those client vlans.
The number #1 problem I have had with local cameras using cloud streaming is DNS.
The browser needs to be able to resolve *.devices.meraki.direct to local devices. Some DNS servers are too old or dumb to know about the special *.direct domain.
You can test if you are affected by such a DNS server by configuring your cameras AND your computer with the browser to use 18.104.22.168 (probably do a reboot to be sure nothing is cached). If it works after that - it's your DNS server.