Nuhvok-Kal, at the time it got destroyed, had increased power due to the Nuva symbols increasing the Bohrok-Kal's power.
Anyway, as far as the question goes:
Short answer: probably not.
According to BS01, specifically the page for the Gravity Shield, the shields Nuhvok-Kal carried could increase gravity up to 1000 times its normal strength.
A black hole, in our world, is generally formed by the collapse of a massive star, which is about 8 times the size of our Sun. Spherus Magna does not have a canon size, but it is generally estimated to be about 10 times the size of Earth, which in turn is about 1/1,000,000 the size of the sun. So the mass of Spherus Magna is (theoretically) about 1/100,000 times the size of the Sun, or 1/800,000. the size of a star that would normally form a black hole. Even if Nuhvok-Kal increased gravity to 1,000 times the normal gravity of Spherus Magna, it would still be 1/800 the gravity "near" a black hole.
Of course, this is estimating a lot of factors (the size of Spherus Magna, and if its mass is comparable to the mass of astral bodies in our world) And Greg could always say "Gravity users can create black holes because I say they can". Black holes, in Bionicle, could work differently from our world.