Can I use 2 in parallel to achieve sensing in 2 locations? More specifically, does the switch care if it sees line voltage on the load side when it is "off"?

Hello, thank you for your question. Only one sensor can be used in a multi-location application; multiple may not be used in parallel. See the below spec sheet for more information: https://assets.lutron.com/a/documents/369666.pdf We hope this helps! If you require further assistance such as learning about more possible control options to suit the needs of your application, our 24/7 support team is here to help. We can be reached at 1-844-LUTRON1 or via email at support@lutron.com.