What folks will say in interview-hiring process doesn't mean that if it doesn't come to pass, that it's because of unlawful discrimination. Just saying (not clear how many places you and your husband have worked at over the years, but it's best to think of employers trying to hire folks to used car salesmen trying to sell cars).
"... all while one of the other technicians were asking him "WHY he bothers to help expand business"."
It would be an awfully naive person not to recognize jealousy and/or disgruntled coworkers here that don't want someone raising the bar on performance vs. unlawful discrimination/harassment.
"... as time went on, the company purchased a couple of small businesses and became tight with money spent. One day around a month and a half ago my husband was told not to go into the Friday morning meetings with everyone else."
If they wanted him to work on other things and are economizing on overtime, it is what it is. The company offering incentives to other people who you seem to imply don't work as hard as he does makes sense, no? He's putting in X effort without promise of more than his pay; they possibly weren't.
It also may be that the other coworkers were griping about his stellar behavior to the point where company didn't want to hear it anymore and decided to take the illogical step of easing your husband out rather than deal with the underlying problems that are their fault.
"From one day to the next he does not know where he is, and all his original irrigation rights and duties were given to a new worker they hired, who is a white man and paid less."
The "paid less" kinds makes sense, no? So why the knee-jerk presumption that race/ethnicity has anything to do with this?
Humans in general when called on the obvious truth, esp. managers that aren't suited for human resources, get defensive. Thus, yelling is a silly, but logical reaction to being called on nonsense.
This "other manager" now being petty and mean and deciding to call your husband Consuela ought to be reported to higher-ups and say that your husband doesn't appreciate this petty behavior ... and, oh, by the way, it can be construed as unlawful harassment. (I presume your husband has politely asked him to knock it off to no effect.)
"Someone told my husband they are trying to get him to walk out so the company does not have to pay unemployment."
Maybe so, but given the employer doesn't "pay unemployment" but only a percentage of tax on payroll amount, I'm not sure I'd listen to that person.
"They now want only cheap labor since the company has spent so much accumulating small businesses."
They are free to lower anyone's wage as they please, so long as they pay min. wage.
Resentment for your husband making more than someone else isn't unlawful. A manager with power to lower or raise wages is stupid if they think your husband has to "accept" working for less. The employer is free to change wages, and if the worker doesn't like it, they may seek life elsewhere.
Unfortunately, suck-ups and mediocre workers can manage to get ahead. Surely this is just reality. It may be that this person is a suck-up or a personal friend of a manager.
"I am not sure what rights my husband has.:"
Plenty, but you need to be more specific.
In your post, I'm not seeing a pattern/thread of them treating him badly because of his ethnicity; I only see that one untoward manager saying things because he's resentful of X or taking something out on your husband (and your husband's free to ask the employer to tell him to knock off with "Consuela" and, if he won't, to file a complaint with the EEOC and state equivalent).
No at-will employee has any job security regardless. If your husband can't abide the situation and can't seem to find a way to work it out with upper management, then he ought to start looking for a place that appreciates him.