The GTOR makes no distinction between how mass and energy affect the curve of geodesic space. They are both lumped into the same source tensor that causes the curves and effects defined by the geometry tensor. So whether mass or energy, or both, which is what I suspect, is at the center, the effects out to the horizon and beyond should be indistinguishable. Both mass and energy (e.g., photons) will be attracted and trapped by the black holes regardless.
What I find interesting, in reading "The Fabric of the Cosmos" by Brian Greene, is the role that stress can play in the space-time effects. Stress is a sort of force field. The type I'm most familiar with is the stress that causes deformation and strain in materials. Turns out that space can be stressed out just like other materials. And when space gets stressed its shape gets deformed, curved. And we all know what that means...the effects we attribute to gravity.
In Greene's book he describes what might have caused the faster than light expansion of the universe very shortly after the big bang, while the universe was quite small. His WAG is that a scalar field, something like a Higgs Field, settled down to zero potential energy shortly after the BB. And that settling process put a stress on space, which caused space to expand very rapidly under a, get this, negative gravity of repulsion.
I bring this up simply because it suggests that stress, say, from a collapsing field, can greatly affect the shape and size of space itself. So who's to say that stress cannot also form black holes like mass and energy can?