On the same account? No. It's not a matter of safety really, it's just that one login will log the other out. In the near future, all of my programs will be able to share cookies so you can run different programs on one account at the same time.
If you mean running the AAAABer on one account and the Island Trainer on another, then it is safe. It's recommended to use proxies so TNT cannot see you are the same person, though.