That's a tough question to answer, because there are so many variables involved, and every person if different. I think it would be proper for you to consider asking yourself some questions in this regard, such as:
Why did the person once hate you to begin with?
Do you feel you were at fault for the person hating you.
If you ever hated someone, could you forgive them, and would it be genuine?
How long have you known the person.
Is the person who hated you family?
What kind of morals does the said person have?
I'm sure there are plenty more questions you could ask yourself about the person, and the situation correlated to why he/she hated you, and perhaps then, you will be able to make a sound decision to trust or not to trust, said person.