With many integrations, there's two options:
PULL: Where the data is PULLED from Meraki, using the APIs
PUSH: where, using web hooks, syslog, data is pushed from Meraki
The Splunk integration appears to be a PULL integration, according to the APIs that it uses:
https://api.meraki.com/api/v1/organizations/:org/devices/statuses/
https://api.meraki.com/api/v1/organizations/:org/uplinks/statuses/
https://api.meraki.com/api/v1/organizations/:org/devices/uplinksLossAndLatency
https://api.meraki.com/api/v1/organizations/:org/networks
https://api.meraki.com/api/v1/networks/:network/devices
I note that the SM endpoints are not included in there
HOWEVER, whilst not impossible, there's a little work for you to do. It looks like Splunk can ingest data using any REST based API:
https://www.splunk.com/en_us/blog/tips-and-tricks/getting-data-from-your-rest-apis-into-splunk.html
And this starts with a simple form to fill in:
Don't forget that Meraki uses a custom parameter for Auth,
X-Cisco-Meraki-API-Key: <secret key>
Which should go into your headers.
Let me know how you get on....