Yes. It is legal. Michigan law does not require meal or rest breaks for adults. If your husband has a disability or needs time for religious purposes (daily prayers), then he may be entitled to additional breaks as a reasonable accommodation. If he needs an accommodation, he should speak with human resources.
If he is a union member or has an employment contract, his collective bargaining agreement or employment contract may have a clause requiring breaks.
Federal law requires that employees be paid for short breaks. Longer, meal breaks may be unpaid as long as employees are completely relieved of their work duties. Other that this, at-will Michigan employees have no break rights.
This answer is provided for guidance only. DO NOT rely on it as legal advice. We DO NOT have an attorney-client relationship. You should contact an attorney in your area for a one-on-one consultation before pursuing any action or making any decisions.
I think Ms. Slack's answer covered all the bases with respect to your husband's circumstances. I would only like to add that in the event his employee manual provides additional break time to be aware that this manual probably can be changed at the employer's convenience.
Also, while not relevant to your husband, it is important for other viewers to be aware that under Federal law employers must provide a reasonable break time for nursing mothers to express breast milk and a place, other than a bathroom, that is shielded from view and free from intrusion from coworkers and the public. 29 USC 207(r).
Also, employees under 18 years of age may not work more than 5 continuous hours without a 30 minute uninterrupted rest period.
I'm licensed in Michigan and only provide an overview of issues you should discuss with competent legal counsel in your state. And my overview is not a substitute for consulting an attorney, especially in addressing a complicated issue like the one you presented.