Can the SIGMA 18-50mm F2.8 DC DN | Contemporary be used with the SIGMA USB DOCK?

Yes. For L-Mount, connecting the separately sold USB DOCK UD-11 to a PC via a USB cable and using the free SIGMA Optimization Pro software enables update of the firmware as well as setting of the focus ring. The USB DOCK is currently not available for Sony E-mount and FUJIFILM X Mount.