vxRAIL VLAN's - Stretched Cluster Issues

[Interwebs27]

Hello all, 

I'm fresh to Fortinet and I'm trying to solve an issue with a vxRail stretched cluster. We have two sites (two seperate datacenters for the moment, with a DR site coming) and a few VLAN's need to be stretched across for the operation. I attempted vxLAN with virtual wire pair, which worked for the ESXi management and iDRAC VLAN's (they share identical subnets on each side). But the issue is getting vMotion and vSAN (different subnets for each site) traffic to pass, which is supposed to be L3, per Dell. I was advised by Dell that running those sensitive VLAN's over VXLAN could cause a broadcast storm, and data loss. I'm not sure of another way with Fortinet to stretch VLAN's across a MetroE connection (L2 connection). I'm currenlty in Central SNAT mode. 

I appreciate any insight or pointers! Thank you. 

[Interwebs27]

MetroE is currently plugged into copper switches