Good Morning Boomer,
You can definitely combine the use of other switched with Meraki, however, you won't be able to add them to the Meraki dashboard. Our organization has several sites using a combination of Meraki and Cisco switches but are only able to get analytics from the Meraki ones. You can however link the two switches to get basic traffic and usage analytics. For example, we monitor VoIP traffic from a Cisco SG300 through our Meraki switches and MX devices.