Nothing with the DHCP server. But as per the article, many clients won't accept such an address. And even if they would accept it, duplicate IP assignments are yet another exciting and hard to debug network problem.

I believe some clients (dhcpcd, networkd) also do the check on their side, so it's possible that they reject the lease and ask for a new one if it's in use.

On the dhcp server, nothing really? But the address isn't usable if this host is arping for it.