The difference between "하지 마라" and "하지 말아" is that 하지 말아 is more indirect, but this distinction doesn't appear in speech since their pronunciation is exactly the same.
Whether you mean 하지 마라 or 하지 말아 people will always understand you mean "하지 마라" in speech, so I don't think you should be bothered to use it knowing the difference.
Be aware that there's no word spelt like "하지 마라요", it's always 하지 말아요.