Software version doesn't seem to be availabe over SNMP. But model and vendor are available, both when polling a device directly with the standard v2 MIB, and when polling the dashboard using the proprietary Meraki MIB.
This is an extract when I walk my dashboard's SNMP tree:
65: devProductCode.12.141.219.23.84.113 MR33-HW
66: devProductCode.12.141.219.25.199.32 MX64-HW
67: devProductCode.224.85.61.209.21.225 MS220-8P-HW
68: devProductDescription.12.141.219.23.84.113 Meraki MR33 Cloud Managed AP
69: devProductDescription.12.141.219.25.199.32 Meraki MX64 Cloud Managed Router
70: devProductDescription.224.85.61.209.21.225 Meraki MS220-8P Cloud Managed PoE Switch
When I poll a specific device I get vendor and model too:
1: sysDescr.0 Meraki MS220-8P Cloud Managed PoE Switch
2: sysObjectID.0 ms220-8p
More info here:
https://documentation.meraki.com/zGeneral_Administration/Monitoring_and_Reporting/SNMP_Overview_and_...
Keep in mind that the SNMP password settings are configured in two different locations depending on whether you're polling a specific device (different password per network) or if you're polling the dashboard (organization wide configuration).
Organization > Settings
Network-wide > General
FYI to poll the dashboard you don't need access to the management VLAN of the devices. To poll the devices themselves you do need access to the subnet.