Using the law of convergence on a Supreme artifact was just Zhao Hai's idea. He might not succeed because the tree demons had minds of their own, while Supreme artifacts did not. Therefore, it was hard to say whether the law of convergence could be used on Supreme artifacts.
As for using it on the undead creatures or the vampires, Zhao Hai had already tested it out, and the effect was quite good. Using the power of law on the undead creatures would turn nearly 10000 undead creatures into a huge skeleton. The combat power of this skeleton was definitely a bit stronger than that of a master in the shattering void realm.
