Thank you for the additional information. Your daughter needs to start documenting all of his drinking and daily habits etc, the emotional and verbal abuse, etc. and hide this documentation from him. Agreed that the child should not be with him unsupervised from what you describe here, and most courts/judges would agree. With a child this age, they take great caution and they do and will order supervised visitation when there is risk of harm.
Some of these questions are for an attorney of course, but your daughter can file a request for a psychological evaluation (with the courts) and her husband will be thoroughly assessed for emotional stability, alcohol and drug use and abuse, parenting, etc.
Also, many supervised visitation centers require drug testing if there is an issue with substance, etc. If he doesn't pass, that will be documented. What I'm saying here is that there are options other than just staying with him. The DUI, will also be solid evidence necessary in your daughter's favor. She really needs to talk with a family law attorney, get informed, and then make informed decisions about this.
There is hope here. Any evidence and/or witnesses to his behavior and drinking are also very important as well. Again, alcohol testing and drug testing etc. can be ordered etc. Your daughter and this child do have rights... so please tell your daughter to seek out legal advice. Typically a psychological evaluation ordered by the court, will easily show that he is not fit and has alcohol issues that need to be addressed before the child is left in his care. Please click green ACCEPT button, otherwise I'm not credited for my help today. I truly with you all the Best with this. Thank you.