I've had no issue distinguishing between the two and working with them on FortiGate but it seems to be different in FortiManager. I see no way of implementing Virtual Servers on FortiManager. The "load balance" option does not expose any functionality for multiple "inside" servers.
It might be worth opening a TAC ticket for this. I checked 6.4.7 and 7.0.4 VM's, Load Balance type didn't show up in 6.4 GUI but can be defined by installing a script to the ADOM DB. It looks like this was added in 7.0.
I only see options for configuring a single external IP/range but this applies to both FMG and FGT GUI.