There is a feature request in for Custom Collision shapes for the base mesh of a destructible with this ticket: Unreal Engine Issues and Bug Tracker (UE-6140)
The unfractured base mesh will only use a single convex hull for its collision. So meshes with holes in them will not have correct collision for these areas. You would want to swap out the mesh and the destructible on impact or within the range of the player to simulate this. Alternatively, you could author your content around these types of issues as well and use some of the flag in the DM editor to allow chunks sections to hold together.
-Tim