An employer may legally establish classes of employees, some of which are eligible for insurance and some of which are not. It would be legal to offer insurance to full time employees but not part time employees; office employees but not shop employees; employees in the corporate office but not employees in the field office; employees in Accounting but not employees in Research and Development; employees in Research and Development but not employees in Accounting; or any other division that does not involve characteristics protected by law.
Once the eligible classes are established, all employees in the eligible classes must be offered insurance, whereas employees who are not in eligible classes need not be.
To determine whether or not your husband needs to be offered insurance, he needs to determine what the eligible classes are and whether or not he falls into one. Only his employer or the insurance carrier can answer this.
It is NOT true, however, that if one employee is offered insurance all must be.