Having a hardline from the hub to the wireless mesh is, to the hub, a wired connection and would work the same as plugging directly into a switch (assuming everything is working properly of course).
Bandwidth isn't much of a concern, but network latency is. Again, assuming your network is healthy, the extra latency shouldn't be noticeable, but it will be there over directly hardwired. This would only impact connectivity needing IP access (Hubitat app on your phone, cloud based services that you've integrated, etc.).
Hubitat has support for a USB-wireless dongle. See this post.
@bertabcd1234 beat me to the punch about the wireless devices.
