FlexCAN is not FlexCAN. There is FlexCAN the (academic?) network architecture http://en.wikipedia.org/wiki/FlexCAN
and FlexCAN the CAN controller, included in some Freescale MCUs (some have MSCAN, some FlexCAN).
AFAIK, Freescale FlexCAN is as vulnerable to babbling idiots as other CAN controllers; I've not read about any special features in that area.