In many states the writ of error coram nobis has been abolished (sometimes long ago) and replaced by a statutory post-conviction petition or some similar remedy. This is a matter of state law. I hope you get an answer from a Virginia attorney.
A writ of coram nobis asks the Appeals Court to address new facts not presented at trial. In Virginia you can file a motion for a Writ of Actual Innocence with the Court of Appeals. There are a few different grounds for filing such a motion and you should contact an attorney to assist you with preparing the motion. Please look at the following link for more information from the Court of Appeals.
A writ of coram nobis (or "coram vobis," which is the same thing) is limited to claims of "clerical error or error in fact."
To answer your specific question, it has not been abolished in Virginia, but it has been greatly limited by case law and statute. It is not the same thing as a Writ of Actual Innocence or a Habeas Petition. For instance, coram nobis CANNOT be used to challenge the validity of a guilty plea or to allege ineffective assistance of counsel. See Va Code 8.01-677; Commonwealth v. Morris, 281 Va. 70, 705 S.E.2d 503 (2011).
Therefore, your son should use the appropriate action for whatever he wants to correct or challenge. Coram nobis is so limited that my best guess would be that he needs to use a different method.