Hello all - noob here. Hoping this hasn’t been asked before - I did look!!
So … have my house wired with Lutron Caseta dimmable wall switches and am using HomeKit to control them. I have the need to add motion sensing to some of these lights. Can I use a Hue hub and Hue motion sensor to control a Lutron light via HomeKit?
Any advice most appreciated.
This forum is for people who are using the Samsung smartthings home automation platform, so the answers that you get would generally be within that context. And they won’t apply if you don’t have a smartthings hub. It’s a very active forum, so it often comes up near the top for Google searches on general home automation questions, but it is specifically for the Samsung brand of home automation.
All of that said, As it happens the specific models you mentioned will work with both smartthings and HomeKit, And I can verify that as long as you have the newest model for the hue bridge and you have all the firmware up to date, you can use a Hue motion sensor connected to that bridge to trigger your Lutron Caseta light switch through a HomeKit automation. We use this at my house. 
https://9to5mac.com/2017/10/03/philips-hue-homekit-tap-dimmer-switch-motion-sensor/