The Earth has a radius of about 6,000 km. If you had a black hole with the same mass as the Earth, gravity would be the same 6,000 km from the tiny black hole as it's just above the surface of the Earth.
The big difference is that an Earth sized planet is pretty easy to visually see, while a black hole onviously is not.
I don't know how navigation between planets and moons is supposed to work in Spelljammer, but if you can see the path of the moon and know where the center of its orbit would be, it should be very easy to stay way clear of the center and be fully safe.
If you just go from one moon to another, the chance of that path leading straight through the center is very tiny. If you get near the center, you'd probably see your ship getting pulled off course towards the center, but you'd just have to adjust your steering a bit to counter for that. Even if you get very close while flying blind, the gravity would most likely thrown you off course as you fly past. Actually being pulled into something to hit it is really hard in space.