If server has strict iptables policy for incoming packets, you would still need to go to iptables allow second port. so if you need to iptables anyway, why just

If server has strict iptables policy for incoming packets, you would still need to go to iptables allow second port. so if you need to iptables anyway, why just not redirect without editing sshd config? the less modifications the better chance to not forget to revert them