Currently the procedural foliage volume will do a ray trace to check for objects it can spawn the foliage on.
InWorld->SweepMultiByObjectType(Hits, StartTrace, DesiredInstance.EndTrace, FQuat::Identity, FCollisionObjectQueryParams(ECC_WorldStatic), SphereShape, QueryParams);
As you can see, it uses the WorldStatic as object type.
I’m using a different collision preset for my landscape, and I’m using a different object type, which doesn’t allow me to use it.
Closed since I’ve decided to create a PR for this my self. Editing in case anyone else will stumble upon this.