Zombies are actually part of TeamB while players are TeamA, so you can make blocking volumes that only zombies can walk through, but there’s a bug that causes zombies to still treat them as solid walls anyway.
In case it helps, there is kind of a workaround for that.
If you place down a thin Blocking Volume as a ramp, low enough to the ground and at the right angle, zombies will walk over it (if it’s too high they’ll treat it as a cliff and avoid it, if it’s too low players can still walk over it from the other side).
If you get the scale/angle right and set the volume to TeamA only, the zombies won’t collide with it and it’ll basically act as a “wall” that zombies can walk through while players can’t.
(the volume in the screenshot is scaled to 0.1 on the thinnest axis and is angled 54.02 degrees)