I was about to ask the same thing. Apart from anything else, DHCP can't rely on that for correct operation because putting the interface in promiscuous mode couldn't possibly help in a switched environment unless you got the switch monitoring to your port, too.

I tell a lie, sorry. I misread the code. It actually tests for network interfaces which are either in promiscuous mode or have a packet socket open on them, and dhcpd does the latter.

So the output is wrong as well as unhelpful...