Both reference System.Windows.Forms.Control
But if you set Port.Parent = null (SerialTools) and Manager.Parent = null (BlueTools) there will be no calls into any Forms component.
If you set the Parent property, events will be called in the GUI thread using Control.Invoke() This however is nothing you should use in a Windows Service.
If you search in this forum, I think you can find some successful cases of using SerialTools in a service. BlueTools is new, so I don't think any service related topics has been posted yet for BlueTools. But there is no known issues.