Hi
what has to be noted in this comunication is following:
ARP entries on a FortiGate configured as whatever on a physical interface can be seen with the corresponding commands shown here like:
# get sys arp
# diagnose ip arp list
ARP entries like VIP ones CAN NOT BE SEEN on the arp list because they are existing in the firewall deamon on layer 4. Example: if you have one public IP on the wan1 and it is physical configured you will see the arp no problem. If you use no a second one and you DO NOT configure the second one as secondary IP on the wan1 (not needed) but instead you configure a VIP based on the second one all works from scratch as long as the second public IP is routed to the wan1 from outsite perspective. If you look to the arp tabel you will NOT see the arp entry for the second public IP because the VIP which has enabled "arp-reply yes" is existing in layer 4 or within the firewall deamon and because of this you will not see a corresponding entry in the command shown here. All commands shown here are based on layer 2 and therefore firewall deamon layer 4 arp entries you will never see. As of information of the Support of Fortinet there is no possibility or a available command which shows this entries.
By the way the same issue/situation we have for routing entries depending client2site (dial-up). This means acutally following: If you create a dial-up and you define for this connection a Office IP Pool (actually a dhcp server which gives after succesfull authentication a IP to the connecting client) you do not have actually to route this Office IP Pool to the IPSec client2site VPN because this entry is done within the IPSec deamon. Of course you can create a static entry which I really recommend because also here the routing is existing within IPSec deamon on layer 4 you will never see the routing entry on layer 3 with the corresponding routing command like:
# diagnose ip route list
Also here based on the information of Fortinet Support there is no command which shows the routing based on layer 4. This circumstances that the dial-up VPN Office Pool has not to be anymore routed and in the background the routing entry is automatically done within the IPSec deamon is for FortiOS 5.0 and higher.
hope this helps
have fun....
Andrea