Our health plan and 401(k) plan have a one-year waiting period before an employee can enroll. We want to hire someone as a full-time employee and provide the person with immediate benefits. The person has been an independent contractor with us for several years, so we will explore credit for prior service for the 401(k) plan.

For this one employee, is there a way we can waive the health plan’s service requirement or offer credit for prior service?

I cannot comment on the 401(k). As for the health plan, the usual answer is no, you cannot waive the waiting period. Check you plan documents for eligibility definition. What you can do for this person is pay the cost of his/her health insurance until they do become eligible.