Do not use source nat off when deploying site to site vpn

Hi all, 

Please clarify me this circumstance. 
We have the topology with requests like this: 
Topology: [PC]---[SRX]----------[INTERNET]----------[Different vendor's Firewall]----[SERVER]

* In encrypted form, via a site to site VPN, between the 2 SRX devices; as shown in the above diagram.

* In unencrypted form, over the Internet by translating private IP addresses into public IP addresses, via Source NAT.

In normally, we will set source nat off for traffic between PC and Server, it takes precedence over source nat interface go to the Internet. 

However, I do not want to use source nat off configuration. So can I set policy to accept the PC's IP public address access Server's IP address on Different vendor's Firewall and do the same on SRX device? 

Thank all