Yes , one operator can have more then one workbasket access.
Workgroup belongs to an organization where as the work basket belongs to a unit in the organization. Every Work basket has a work group and every operator has a default work group and can be authorized manager of many workgroups within the organization .
Ex. Operator's default work group is WG1 , and there are three workbaskets WB1,WB2,WB3 mapped to the operator's profile . The workgroup of workbaskets WB1,WB2 is WG1 and WB3 is WG2 respectively .
The operator can receive assignments from all the workbaskets using get next work , but the default work basket lists which is displayed is based on the active work group . If the active workgroup is WG1 you will see WB1,WB2 and the default workbasket of the workgroup and if the active workgroup is WG2 you will see WB3 and the default workbasket of the workgroup.
For further relationships between work group and workbasket you can refer the below link.