IPSec VPN over ethernet path. Is it recommended ?

Guys,

I have 2 x FortiGates that would act as VPNs peers. The medium is a METRO ETHERNET owned by some third party provider.

The FortiGates are running FortiOS 5.4. 

What is weird to me is the fact that the path between them is actually a Metro Ethernet network crossing some third party provider. You usually create VPNs connections over a unsecure L3 networks.

When you go to FortiGate GUI it seems it's possible configuring this IPSec VPN using the IPsec VPN Wizard (using remote peer on the same subnet), but I'm wondering is this is practical and it's a best practice to encrypt traffic over a Metro Ethernet PATH using 2 FortiGates....  

THANK YOU ALL