I just find out a way to do read-only checkbox in a grid and like to share with you.
var grid = initGrid();
grid .load(dataSource, function(){
grid .forEachRow(function(id){
grid .cells(id, INDEX).setDisabled(true);
});
});
The trick here is after the grid load data from a data source, in the callback function, immediately disable the checkbox by going through each row of a grid (i.e. forEachRow), set the cell with the INDEX (where your checkbox is) to disable.
Hope it helps.