Hi,
I suggest that you add more specific design details, so that other users can help you.
For Example- We have client on the remote end that require us to hide source address behind a single IP address.
You mean hide the LAN behind the VPN-FW behind one IP or even hide the public IP of the VPN Firewall behind some other IP? These two are totally different.
By default, all VPN traffic will be sourced from the VPN FW public IP. If you need to NAT even the actual traffic encrypted by the VPN FW, you will need to setup NAT on the VPN FW.
If NAT will be on DMZ FW, NAT-T will make things easy. Otherwise, you will need to setup 1-to-1 NAT, tweak with the IKE ID etc.,
Even if all this is sorted out, you will need to allow UDP500/4500, ESP, AH etc., on the DMZ FW - between VPN FW and checkpoint.