This option is an homage to the origins of NetTools. NetTools started off life as a utility call PDCTest back in NT4 days, it was a utility to find the PDC in an NT4 domain, a few extra tabs were added as more options were included. It continued this way for a few more years, however the number of tabs was getting out of control and in back 2005ish I redesign the interface and NetTools was born. I left NetGetDcName unchanged and as a result it looks a little out of place, like RunAs which has remained unchanged. PDCTest name still existing in some of the error dialogs and ICMP data blocks.
The test still works in an AD environment and will return the PDC of the domain, however, completing both the server and domain fields can cause strange results.