I received word that the Selection command input does not behave correctly when it's used in a table so it was blocked in the API. I was also told that the button row command input also has a similar problem. I need to document these limitations.
I think this is because these two inputs contains more than one component. The selection has the arrow button, text to display the number of selections, and the "X" button to clear the selections and the button row contains multiple buttons. Apparently the table wasn't designed to handle this and would have to be enhanced to support it.
Sorry for the bad news. I suggest looking at some of the Fusion commands, like Loft, to see how that handle selection in conjunction with tables.