I'm going to say no based on what I've found/not found. (feel free to correct/educate me if I am wrong anyone)
Meraki is starting to incorporate Cisco Umbrella if that helps you in any way, as well as being able to specify your own DNS etc.
I'm not sure the question applies as Meraki doesn't have a DNS server product. The MX and MR can act as DNS proxies, but that's about it.
DNSSEC can be applied to sign domain records. I presume n168.meraki.com owned by Meraki.
Oooooh! I misunderstood. You're asking if Meraki has DNSSEC available on their own domains. Gotcha.
It doesn't look like they support it.