They (usings) are not gerunds but participles, called present particples. Both of them function in your sentences as post-modifiers. That is, they are respectively modifying the preceding nouns (=companies).
And you can simply use relative clauses to substitue for them.
1 Companies (subject) that use fear market is a wrong practice.
2 I disagree with companies (object of "with") that use fear marketing to seel products.
Notice: Neither a native speaker nor an English teacher.
Natives may be coming soon.
Student or Learner