1) does anyone know if it possible to zoom and pan when using v.digit
without closing the line/area?
No, you must stop digitizing to move the view. Sure would be nice if it
did though.
The QGIS-GRASS digitizer should be able to do it.
2) Is there any command to create a vector line which links vector
points automatically?
Two ways:
In v.digit you can move the endpoints close together and they will
'snap' closed. Doesn't work while digitizing the line, only after.
Sure would be nice if it did though.