Let’s see if I can be clear. Supersymmetry makes testable predictions, for example, the existence of supersymmetric particles. No supersymmetric particles have been found, yet, but their existence is testable. (Of course, their nonexistence isn’t, really. You can’t rule out that they are just a little more massive than anything we can test.) Supersymmetry does not predict the masses of the supersymmetric particles. If supersymmetry were not a broken symmetry, then it would, but supersymmetry is broken. String theory is not inconsistent with supersymmetry, and as a more encompassing theory could presumably could predict the masses of supersymmetric particles, but to the best of my knowledge, no one has successfully done so.
The situation is similar with the Higgs boson. The as yet unseen Higgs boson is not a prediction of string theory. The Higgs boson was introduced to give masses in nonabelian gauge theories, like the Electroweak theory and QCD. Supersymmetry would incorporate those theories and string theory supersymmetry. But, the existence of the Higgs boson is a nonabelian gauge theory prediction. String theory has not produced a Higgs boson mass prediction.
As near as I can tell, the black hole work is not particular to string theory, it is brane theory work. It is, in principle testable, and string theory motivated brane theory, so you can claim that is a prediction of string theory if you want. Unfortunately, I am too long removed from the field to know more than what I’ve read in Physics Today (the APS monthly, which I am over a year behind on) or Scientific American. I do not believe, however, that the results can be called a prediction of string theory. (For example, quantizing spacetime yields the same result.) If the results were sufficiently detailed, and string theory dependent, to truly explain how a Hawking radiation photon comes into being, then I would call it a prediction of string theory. (Hawking’s prediction of radiation involves some arguments, that while reasonable, don’t explain everything. For example, the photons that start on the event horizon must have an infinite energy, which is impossible. Last June’s (July? May?) Physics Today contains a nice article on that, and using fluid experiments to investigate it.