Site to site VPN to a vendor site with the same subnet at both ends

Hello all,

we are looking at a situation where we need to set up a site to site VPN to a vendor who is using a Fortigate gateway, and the same subnet is being used at both ends.  I have reviewed the below link which covers this situation for Sophos to Sophos, but I'm just wondering if anyone has had any experience with this with a Fortigate at the other end?  Unfortunately, we don't control the vendor end (naturally).

NAT with route-based IPsec when local and remote subnets are the same - Sophos Firewall

Does anyone know of anything to look out for with connecting to a Fortigate?  We are using an XG210 at our end.