Short answer: Yes, for bona fide employee classes (like salaried vs. hourly) applied consistently. Whether you can tilt the design toward higher-paid employees depends on how the plan is funded: self-insured plans and pre-tax cafeteria-plan contributions face nondiscrimination limits, while fully insured plans currently do not.
An employer can offer different plans or contributions to different bona fide employee classes, such as management vs. hourly or full-time vs. part-time. Within each class, the terms must apply uniformly and cannot be varied based on an individual’s health.
Whether you can structure the design to favor higher-paid employees depends on how the plan is funded. A self-insured medical plan cannot discriminate in favor of highly compensated employees under IRC Section 105(h). If employees pay their share with pre-tax dollars through a cafeteria plan, Section 125 applies its own nondiscrimination tests. For a fully insured plan, the comparable Affordable Care Act rule has been suspended since IRS Notice 2011-1, so a design that favors higher-paid employees is not currently penalized there, though that could change if regulations are issued.
Insurers also set their own underwriting rules on how many plans and what class definitions they will allow.