Get legal advice ASAP. He may need to go back to court and have the plea renegotiated under Padilla v. Kentucky (google it). It is a deportable offense. Good luck, but you need help.
You should consult with an immigration attorney for a review of the actual charge and conviction ASAP. A determination of the immigration consequences is necessary to evaluate his chances for release from ICE custody and likelihood of deportation. DV comes in different forms and shapes and can be grounds for removal of permanent residents.
You need to collect all of his criminal case information and provide the information to an experienced immigration attorney for a legal opinion. Immigration law treats criminal adjudications differently than does criminal law. He should do this asap as he may be able to gain relief based on recent USSC case of Kentucky v. Padilla. Good luck.
Legal disclaimer: The statement above is provided by CC Abbott is based on general assistance and not intended to be a legal opinion because not all the facts are provided. The person requesting information and all others reading the answer should retain an attorney who is permitted by the state bar within the jurisdiction who can examine the complete facts and provide a legal opinion on your case. All information provided in the above answer and other information provided by CC Abbott does not create an attorney/client relationship within any state of Federal law.