Can't you apply a 'trigger_remove' to the walls inside/around the spawns to stop the hooks from attaching to them?
Also I think 'func_vclip_physics' can block them as they travel though the air as well, a couple of those filtered to the hooks over doorways might work.
EDIT: Reason you should use a filter with the 'func_vclip_physics' is because otherwise it would effect other projectiles like grenade pills and sandman balls. You only want it to effect the hooks, hence the filter.
It probably wouldn't hurt to apply the same filter to the 'trigger_remove' as well.