The public-ip argument passed to binary zetaclientd is used for TSS p2p network communication. In this case, the go-tss library needs to be modified in order to support hostname, because the go-tss asks for an ExternalIP in its network config struct (see the struct below). Internally, the go-tss wraps the IP address in a pattern fmt.Sprintf("/ip4/%s/tcp/%d", externalIP, port) to form a Multiaddr object here, so I believe supporting hostname would be more a go-tss library feature instead of ZetaChain protocol.

type NetworkConfig struct {
	common.TssConfig
	ExternalIP       string
	Port             int
	BootstrapPeers   []maddr.Multiaddr
	WhitelistedPeers []peer.ID
}