Can I drive my work vehicle with an Ignition Interlock License?

Yes. There is an exception for work vehicles. (i.e. Delivery Truck) If your employment requires you to drive a vehicle during working hours that is owned, leased, rented, or the temporary responsibility of your employer, it may be exempt. The Washington State Department of Licensing must have a signed Employer Declaration on file. The issue is whether the employer would still employ you. (i.e. insurance coverage issues) I think this would depend on the company and be determined on a case-by-case basis. Some big employers are self-insured. See link for employer declaration. Employer Declaration