Yes it should be possible. However, since there is no matching keys between source and target Logical Units, you will have to write new transformation method and apply it.

Good, I was afraid that the object connection had to really exist to be able to do the roll up.

Can we solve this simple by adding a custom field on the WorkTask holding the parent WorkOrder's Activity_Seq? In stead of creating a transformation method?

I think it has to exist, if "roll up" means what I think it does. It might risk being a quite slow feature to roll up both "real" and transformed connections.

A transformation method could do the roll up though, if the amount of objects and documents related to the project is reasonable…

Then there's always the option to actually duplicate the document connections using a custom event or customization.

I did not get an answer to this: “Can we solve this simple by adding a custom field on the WorkTask holding the parent WorkOrder's Activity_Seq? In stead of creating a transformation method?”

What's your thinking about that? I don't follow…