No VCDS/VAGCom/VAS-PC required for reverse park sensors.

Only wiring you need to splice into is the black wire with blue trace, which is the reverse light wire. I think it's on the left side rear corner. The grommet is pretty much behind where the number plate is, behind the bumper.

As for splicing in, Volkswagen recommends duraseal crimp connectors. Cut the wire you're tapping into, strip the ends, strip the end of the wire you're adding, twist it into one of the other wires, join it all with the duraseal crimp connector, and apply heat to seal the whole lot.