Mr. Marx and SuperRadioFan have it correct.
A hostile work environment has no relation to what you are paid as an employee or any change in that salary no matter what. It relates solely to comments, discussion, harassment, language, berating, off-color remarks, etc. mad to, buy others in the workplace, not specifically applied to you.
As an "at-will" state and without a specific employment contract pertaining to your specific job services, you can be let go at any time for any reason. Changing salary is not protected, unless by contract ... and even then, if renegotiated by one or the other parties.
You do not get unemployment unless you are actually unemployed. You make no money and were terminated from your job. You quit, you lose. And getting a lawyer is not as easy as it looks and they do not take labor law on contingency ... you pay for it.
If you are terminated for someone making more money than you ... there's nothing wrong with that. They, in the eyes of an employer, may be seen as more worthwhile for the job offered and there might be another job description. Secondly you finding out that someone made more money than you doesn't happen.
If you were fired and someone came in to make less money than you, that's legal, too, based on seniority, job description, financial situation situation. Nothing wrong with that.
Now, if the job is open between you and to someone else and someone is hired at a lower rate for the same job ... you can then file for, possibly, job discrimination if you fall within the protected areas of "race, creed, color, sexual orientation, religion or nation origin." It is your job to prove discrimination and that is not cheap.
If you accept employment, including a job down the road that you may feel that you don't want to do, you either do it or quit. If you have a specific contract or work agreement, you may challenge that added work with the employer, but all they have to do is rewrite the agreement. Whether you accept it or not is up to you.
Again, as for the original question -- an employer can cut your salary to "$0" before you become eligible for unemployment insurance and, in any case, you'd be out the door because they have to terminate you. If they cut your salary to "$0" and you stay, that won't happen, by law. You'll be kicked to the curb. Ploys are legal, incidentally. It's all about how it affects you in the end.