That is correct. The Meraki Go app will only scan Meraki Go hardware, and let you manage it in the app.
Having all Meraki Go hardware gives you that single pane of glass and ease of management in one place. However, if you are looking to toss another vendors switch, access point, or firewall in the mix - all that is required for the Go hardware to function is a valid IP address and an internet connection (to reach our cloud controllers which dish out the configuration to the device).