Again, sorry to hear this happened. I'm going to give you some information about what whill be happening with his case in the coming future, and what I think the odds are against him being violated for his parole.
There will be a parole violation hearing scheduled in which the prosecutor will have to prove the violation occurred, that is, they will have to prove that the assault with bodily injury did in fact occur. In order to prove this, they can use witness testimony, and any other evidence they may have, such as pictures of injuries. If there were no visible injuries (since you stated the incident was limited to hair pulling) then the prosecutor will have difficulty in proving that the incident did in fact occur, if you do not cooperate with them and testify against your boyfriend.
Of course, if you feel your safety is in danger, then you should cooperate with the prosecution, or at the very least use this as an opportunity to leave the relationship. If however, you do not feel you are at risk, as you stated above, and want to continue with the relationship, then my recommendation would be to decline to testify against him and to let the prosecutor's office know that you do not wish to press charges and that you do not want to cooperate in helping with their case.
The end result of whether or not your boyfriend will receive a parole violation rests in the judge's discretion. However, I do think that if there is no additional evidence, and if you do not testify for the prosecution, they will have a hard time proving a violation against him. Keep in mind, you can also hire a lawyer to represent him in his parole violation hearing, which I would recommend just to ensure that there is a qualified attorney fighting in his corner, unfortunately without an attorney it's easy to be taken advantage of in our current legal system.
I hope that helps! Please let me know if you have any other questions. Also, please take a moment to rate me using the stars as this is the only way experts are compensated for our time here on 'just answer'. It doesn't cost you anything to rate me, and we can still continue our conversation for free after. Thanks!