IF they are using FP during evening EMH at a particular attraction, then I believe the FPXC will work fine. However, they do not always use FP - it depends on the attraction manager and the expected crowds.
If FP is not in use, then the FP line is generally closed and unstaffed, and you probably would not be able to use the FPXC. But you might be able to ask a CM and they may be able to accommodate you anyways - its pot luck at that point.