“Gort, I don't see how either of those would work in combine. ”
You don't see how they'd work?
Simple: they're as visible as a sun. They give off radiation, just as a solar mass does.
In fact, most black holes (of the size we're discussing, which is multiple hundreds or thousands of solar masses) give off more energy than that many solar masses.
The term "black hole" is a complete misnomer. Hell, we can detect black holes in other galaxies, they're so powerful.
And if their presence is known mostly to only a handful of experienced pilots and/or players, then they seem a completely capricious means of weeding out less experienced players -- especially if you can only detect them through their gravity, which, as is admitted above, may or may not be beneath another nearby gravity-producing entity.
And if we're talking only "small" black holes, the kind of single solar mass, then the only method capable of producing them is a supernova, whose effects are also easily detectable.
Everything in this galaxy is mappable, from asteroid fields to trading stations. If our nav computers can store information on items as small as man-made stations and 1x1 entities, if our sensors can detect small craft like fighters and even satellites, then there is no intelligent reason why a massively powerful object like a black hole should not also be included in such displays.
Nor is there any reason why any rationally-designed navigational system could not blurt out a warning to avoid that violently powerful gravity disturbance ahead.
I mean, even a 21st Century combustion-powered ground vehicle can now detect a tricycle in its blind spot.