Confirmed working over here 
#Woobm-USB How Much Can It Do?
[http://forum.mikrotik.com/t/woobm-usb-how-much-can-it-do/112274/1]
And here:
#USB serial adapters
[https://wiki.mikrotik.com/wiki/Supported_Hardware#USB_serial_adapters]
Maybe I am missing something, but over here:
#Manual:Port
[https://wiki.mikrotik.com/wiki/Manual:Port]
It says:
Serial and USB ports can also be used to:
- connect 3G modems;
- connect to another device through a serial cable
- access device connected to serial cable remotely
and my hEX S | RB760iGS has an USB port …