You could try table.addCellPreviewHandler(). Basically the handler is called before a cell receives the event in its Cell.onBrowserEvent() method. The PreviewEvent gives you access to the event type, column index and the row value. So you could check for the focus event and the column and then do your stuff with the row value from outside the table.
Cells just render strings so event handling is more low level than in widgets.
-- J.