Can I give guest hub access to just one of my hubs

If you’re looking to automate codes for your rental property check out this app

There are other apps and device handlers which are useful for rental properties. For example you can use the enhanced zwave thermostat device handler with a GoControl or Honeywell thermostat to limit the maximum heat and minimum cool temperatures for the thermostat so folks have some but not unlimited flexibility.

There are SmartApps for temperature and humidity management as well, a door and lock synchronizer and more.