Depends on how deep that person's hatred is and the kind of person he/she is.
One person that I know of who has some unresolved issues with his co-worker asked him for some help. Other people will probably immediately say "NO" if their enemy asks them for help, but he is such a kind person that he still helped his enemy.
The hatred is still there though, but he still helped him despite of everything. I believe this somewhat proves that when people see that you are in a desparate situation, people regardless of enemy or not will still help other people.