Can a Hubitat hub be plugged into a switch (which is plugged into a router) or does the hub need to be plugged directly into the router?
Yup, its how I have both of mine
Although some switches have given them some trouble. Which switch do you have? May be best contacting support to see if its a known issue switch?
Good advice! Especially because there is a LAN auto-negotiation patch that can be sent to your hub by support to deal with problematic switches.