There is no difference between these two fallacies.

Just finished the book and it seems that, "bulverism" is exactly the same as an ad hominem, stating that an argument cannot be true because of the character.

A great example of an ad hominem is Saying that someone who doesn't have a uterus cannot have an opinion on abortion.

A great example of bulverism is saying that someone without a uterus cannot have a valid opinion on abortion either.

Even when two of these fallacies are described, ad hominem (abusive) just means to discredit an argument by talking about the character, where as bulverism is said to be the same, a combination of the genetic fallacy (because of the character being the source) and circular reasoning (why they are wrong).

In an ad hominem, the genetic fallacy could be shown when the person criticises who is talking by simply trying to argue by saying, "Oh look who is talking, the guy that doesn't even go to school", and circular reasoning where the person using the ad hominem ASSUMES that that must be the reason why are they not correct.

So is there any difference whatsoever?

The ad hominem (abusive) generally is an attack on one's character and bulverism uses the genetic fallacy where the origin of the argument is evaluated rather than the argument itself. So while they can overlap like in your example, they don't have to. For example, if someone dismissed an argument because it came from the Bible, that would be the genetic fallacy, not an ad hominem.