No 'onHover' event exists in datagrid plugin. You have to achieve this functionality manually, please try the code below:
$('#dg').datagrid({
onLoadSuccess:function(){
var target = this;
var opts = $(target).datagrid('options');
opts.finder.getTr(target,0,'allbody').each(function(){
$(this).bind('mouseenter',function(){
$(target).datagrid('selectRow', $(this).attr('datagrid-row-index'))
})
})
}
})