Ok, here is the Jump pack rule
2.1.7 Jump Packs
Some units are noted as having jump packs. These units are equipped with special devices that allow them to fly for short distances, usually in a series of long ‘hops’. Units equipped with jump packs may ignore dangerous or impassable terrain as they move (they jump over it). They may not land on impassable terrain, and if they land in dangerous terrain they must take a dangerous terrain test. Units equipped with jump packs may also move over other friendly units as they move, but may not land on
them. Units with jump packs are affected by enemy units and zones of control normally, and cannot jump over enemy formations. Infantry find Cliffs 'impassable'; and Marsh, Rivers and Barbed wire 'dangerous'. Jump pack troops may jump over these, but, if they needed to enter such terrain (eg to assault enemy troops) then they must take a DT test like anyone else (both to enter and to exit).
Note (Hena), units may elect to move cautiously through dangerous terrain by only going 5cm per move, which allows them to re-roll the DT test if they fail, but they still take the test.
This would affect Warp Spiders in the same way as other infantry. Infiltrator merely allows them to extend their move when assaulting (and mimics the short 'warp' jumps that they can perform), while Jump pack allows them to bypass terrain as they do so, but does not exempt them from the DT test if they end up in the stuff.
Edit - OK so Hena got there first, but I got the quote again
