Remote SSL VPN network is the same with the central Server network

I'm assuming you're using tunnel mode with FortiClient. Then the problem happens on the client side since it sees the destination is on the local network. I haven't done this but I would think it would work if you assign a different subnet for the servers then set 1-to-1 VIP (you might need SNAT w/ ippool as well if the sever side needs to initiate sessions toward the client) with the real IPs, then apply them to the policy from ssl.root to the server interface.