これが私のコードの一部ですが、このようにして、第3レベルのView Controllerを押すと、タブバーが表示されません。
//at first level
SecondLevelViewController *_2vc = [[SecondLevelViewController alloc]initWithNibName:@"SecondLevelViewController" bundle:nil];
_2vc.hidesBottomBarWhenPushed = YES;
[self.navigationController pushViewController:_2vc animated:YES];
//at second level
ThirdLevelViewController *_3vc = [[ThirdLevelViewController alloc]initWithNibName:@"ThirdLevelViewController" bundle:nil];
_3vc.hidesBottomBarWhenPushed = NO;
[self.navigationController pushViewController:_3vc animated:YES];