Yes, a node can have multiple parents. I think using node().addChild(…) will not remove the node from its previous parent, but check the list of parents to be sure.
Of course, this results in the node being visited more than once during rendering, if both cells are being rendered, causing it to be rendered twice. This is how instancing works.
It also means there are two possible NodePaths to the node, which will give different properties depending on the properties assigned to the parent.