What IS his diagnosis?

Your husband is not being "treated". He is using a workbook, without reflecting on the lessons with a therapist. He needs therapy sessions along with the workbook. He should be addressing his feelings of rejection with a therapist, and he should be working on how to appropriately and respectfully respond to those feelings without abusing you. The DBT workbook did not stop him from escalating the abuse further, and from abusing you in front of your child. Abuse statistically worsens and escalates over time. So what will it be next time?

My husband has ADHD, depression and anxiety, but I am not analyzing his mental health issues in order to understand and dissect his abusive behaviors. He is abusive, period, and I told him I will not put up with his abuse any longer. I have PTSD, anxiety and depression, yet I am not abusive.

When you say you "suspect" it's something more, you are trying to play psychologist with him, rather than addressing the abuse directly. It's like you're dancing around the real issues, dissecting and analyzing it to death, spending lots of time on it trying to figure it all out, which is circumventing the real issue at hand. He is increasingly abusive, and it's going to continue as long as you continue to not address it directly.