The videos people put up of inserting the Juggernaut flood into High Charity show they can actually "die." (in truth they can't actually die, since they were never given a death sequence. On all the videos, they just stop where they are when you kill them.) In the "field guide" thread there is no information given on the flood or what custom weapons they may wield. (but there was nothing in any of the Halo manuals about them either.)