The two part plate with the elastomer insert in the middle is the Vist WC plate that Head (and Fischer?) used to use on their Race Dept. skis. Head & Fischer now use the Tyrolia Raceplate RDX instead, which is also a two part flexing plate but not joined in the middle.
FreeFlex bindings are in no way dependent on a plate. You can mount them flat, on either of the plates mentioned, on the CP13/SP13/WC Jr CarvePlate style pre-drilled plates.... anything goes.
In general, FreeFlex bindings are used on higher end race/carving skis, and in general these have some kind of plate but there is no dependency. Your shop is wrong.