In my experience just because the DC isn't in the domain_krb doesn't mean that vIDM doesn't use it for other things. Check your logs and I bet you will see the down DC in there and vIDM trying to connect to it. This has been a serious issue with our site as we have a lot of DCs in our environment. Another major issue we've seen is that when the first DC in the list goes down, vIDM does not check the second or third or fourth. Supposedly these issues have been resolved in v3.3, but we have not upgraded to see if that is true or not.
