Is printing to a USB-printer using LOCL from SAP possible?Yes, as long as this printer is defined on local workstation, it will work.
SAPLPD doesn't care on how the printer is connected, as long as Windows can print to it, SAPLPD will do its work.
Define one new device, also consider giving :
Device type as SAPWIN
Host Printer __default (yes, two underscores default)
Access Method : F
Make sure your desktop/PC Windows default printer is set to this USB printer.