I had a similar issue and had to write my own code to target a specific domain controller rather than using the built-in workflows. I'm using vro, not vra, so maybe there's a difference but here's what I did:
Add all your domain controllers in vro then make your own scriptable task step to find the domain controllers and loop them through/target a specific one. This little piece of code, not pretty but it works, pulls all my domain controllers, matches against a specific one, then runs a search. After that I can take my ADcomputer and pass it to the destroyElementRecursive action and delete the computer account on the specified domain controller. In my case I know what location i'm working against so I know what DC I want to target but in your case I guess yo uwould just put the code for the getComputerAD into the for loop perhaps.
var allAdHosts = AD_HostManager.findAllHosts();
var myDCtoUse = "abc001";
//pick the one we want to target
for (i = 0; i < allAdHosts.length; i++) {
if (allAdHosts[i].name == myDCtoUse){
foundAdHost = allAdHosts[i].id;
}
}
//get AD host object from the id
var adDc = AD_HostManager.findHost(foundAdHost);
ADcomputer=ActiveDirectory.getComputerAD(computerName,adDc);
