No. In Washington, the law sets out specific guidelines for when an employee must take his or her 10 minute paid rest breaks and 30 minute unpaid meal breaks. Although the law does not specifically address or prohibit an employee from combining rest and meal breaks, because the law requires that an employee not work more than 3 consecutive hours without a 10 minute paid break, for instance, an employee on an 8 hour work shift is effectively prevented from being able to combine his or her rest and meal breaks within the confines of the law. To be sure, however, for your particular situation (particularly if your employee is on a different length or unusual work shift requiring more breaks and meal periods) you can map out breaks based on the time tables set out in the law and see if there is a way that the rest and meal break would coincide while still assuring the employee receives all of his or her rest and meal breaks at the appropriate times required by law.
[This is not legal advise - you should consult an attorney to address your specific situation.]