This thread raises a most interesting possibility, but if such a cloaking capability exists, then I would think they would disguise themselves by pretending to be a Sun or Star to limit the effects needed to actually fool someone from the black hole effects that a black hole would have to have to properly fool anyone.

One reason for them disguising themselves as something 'taking in' stars as it were is that they may be able to gather energy from sucking up stars and matter to sustain their craft/whatever they're hiding!

To disguise themselves as a star would surely mean spending energy in the form of light, or at least that's what we understand about this kind of stuff! I wouldn't be surprised if the universe worked in a completely different way to what we think.

Very interesting thread OP, black holes have always intrigued me as demonstrating the unharnessed power of the universe. I'd be surprised if they were hidden craft, but we know almost literally nothing about the universe I guess.

as an interesting add on to previous article, here is a reference for kardashev scale:

In 1964, Kardashev defined three levels of civilizations, based on the order of magnitude of the amount of power available to them:
Type I: "technological level close to the level presently [1964] attained on earth, with energy consumption at ≈4×1019 erg/sec.[2] Guillermo A. Lemarchand stated this as "a level "near" contemporary terrestrial civilization with an energy capability equivalent to the solar insolation on Earth, between 10 to the 16 power and 10 to the 17 power Watts."[3]
Type II: "a civilization capable of harnessing the energy radiated by its own star (for example, the stage of successful construction of a "Dyson sphere"); energy consumption at ≈4×1033 erg/sec.[2] Lemarchand stated this as "a civilization capable of utilizing and channeling the entire radiation output of its star. The energy utilization would then be comparable to the luminosity of our Sun, about 4 x 10 to the 26 power Watts."[3]
Type III: "a civilization in possession of energy on the scale of its own galaxy, with energy consumption at≈4×1044 erg/sec."[2] Lemarchand stated this as "a civilization with access to the power comparable to the luminosity of the entire Milky Way galaxy, about 4 x 10 to the 37 power Watts."[3]

It is most obvious type 3 civilizations COULD very well and plausible be cloaking via black holes, or it some type of energy device.
If you accept the kardashev scale, it should be a obvious possibility.