Yes, USB3.0 camera can use with USB3.1 port.
However, camera operation is USB3.0 operation.
(When connecting with USB3.1 port, camera cannot operate faster more than USB3.0 performance)

USB cameras can use with Windows XP environment.
Slow frame rate, or image could not acquire image even recognize USB camera may occure depends on performacne of USB host controllor and CPU on Windows XP environment.

It can be checked “Universal Serial Bus Control” in “Device Manager” of Windows.
 
“USB3.0” includes in name of USB host controller if USB host controller is USB3.0 host controller.
“USB2.0” or “USB Enhanced” includes in name of USB host controller if USB host controller is USB2.0 host controller.