Yes, We can add the same partner in Multiple Workflows.
We can directly add it while importing CSV file or by following steps.
Step 1 – Select "Edit" option from "Actions" button at the edge of partner's list .

Step 2 - Now, as edit page displays, select Service Workflow field and choose multiple workflows.

We can directly add it while importing CSV file or by following steps.
Step 1 – Select "Edit" option from "Actions" button at the edge of partner's list .

Step 2 - Now, as edit page displays, select Service Workflow field and choose multiple workflows.
