Is saying "get tough with" different from saying "be tough with"?
No, "get tough with them" here means the same thing as "be tough with them". The main difference in this case is that "get tough" is expressing that he will be tough, so it describes future tense. To "be tough" expresses the state of being tough, which is present tense. However, "be tough" is often the most common phrase to use, even when describing the future. Ex: I will have to be tough with them.