Someone posted a link to the AutoVPN document, which seemed to not be relevant.. but it did have this snippet:
"Device-to-cloud communication is encrypted twice: once via Meraki proprietary encryption and again using TLS. "
https://meraki.cisco.com/lib/pdf/meraki_whitepaper_autovpn.pdf
I am presuming TLS over UDP port 7351 = DTLS... but would be nice to know for certain.