Is hacking a crime in the US?
Hacking is covered under a multitude of laws in the United States. While there are federal laws that deal with the issue (usually where the hacking has caused a DDOS or other serious damage to a computer system, or has stolen sensitive information which in and of itself would be illegal to possess under U.S. laws) each state has its own set of "computer trespass" laws. Jurisdiction is based on where an act is committed. For example, if you live in Arkansas and attack a computer system in Oklahoma, the state of Oklahoma can prosecute you under their state law, and the state of Arkansas can commence a separate prosecution under their law as well, and within theory, the federal government is entitled to a third separate prosecution. Double jeopardy won't apply since the Double jeopardy rule requires a person to be charged twice under the same exact statute with respect to the same conduct- but notably, does not prohibit charging multiple statutes for the same line of conduct.
Generally, yes. Black hat(unethical) hackers are subject to the Computer Fraud and Abuse Act.
White hat(ethical) hackers are granted permission from organizations to help them better their defenses and are not subject to criminal charges.