If the federal employee who generated the purchase request has any type of relationship with the other federal employee, there is a potential for a conflict of interest. If the federal employee who provides the item or service during their non-duty time has no personal or professional connection to the requester— and there is a good business case to make award to a supplier who happens to also be a federal employee— there might not necessarily be a conflict of interest. However, I am not legal counsel. In order to proceed with confidence, you need to check with your organization's legal counsel.