In Ext.ux.grid.CheckColumn, the editable config option is ignored because processEvent is used instead of an Editor. The processEvent function could be modified to include a check for editable.

Code:
    processEvent : function(name, e, grid, rowIndex, colIndex){
        if (this.editable !== false) {
            if (name == 'mousedown') {
                var record = grid.store.getAt(rowIndex);
                record.set(this.dataIndex, !record.data[this.dataIndex]);
                return false; // Cancel row selection.
            } else {
                return Ext.grid.ActionColumn.superclass.processEvent.apply(this, arguments);
            }
        }
    },
A workaround until this is addressed in the Ext code