(Evil and Chaos @ Aug. 31 2006,21:16)
QUOTE
As far as 40k goes, the following do not require synapse (* denotes a creature with independant / synapse status in Epic)
Hierophant *
Hierodule (Both types)
Trygon
Harridan *
Carnifex
Basically, this is because they all have the
fearless rule in 40k, which means they automatically pass any ld. tests they are required to make.
However Epic relegates independant status back to only the Hierophant, as having a dozen independant Carnifex broods running around the table would just be too scary.

Also, the Harridan does not have Synapse in 40k, but it's a fairly logical assumption to allow it to have Synapse in Epic, due to fluff, and the mechanics of the 40k flyer rules meaning synapse would be hard to represent.
Fearless doesn't mean they don't automatically pass Ld test, merely morale tests. This has been reafirmed in the nid FAQ where it states that carnifex do take instinctive behaviour checks, but if they fail they don't fall back but lurk instead (which makes no sense since the options are risk failing IB or lurk).
Naturally FWs FAQ goes against this and says that fearless creatures ignore IB.