Is it exactly the same burial service and requiem liturgy that is celebrated in the Traditional Roman Rite? I say this because some of the prayers make reference to purgatory (according to Catholics). The Requiem Liturgy is very ancient, some prayers come from the apostolic times.
Can you post a link with the Requiem Liturgy according to the WRV?
The Requiem and Office of the Dead do not make any direct reference to purgatory that I've seen, other than requests to deliver the deceased from hell and to cleanse them of their sins, which is no different than that found in the Byzantine prayers for the dead. From what I've seen, the Office and Requiem are taken with no changes from the Catholic texts.
Here is the Office of the Dead
, and here are the Requiem propers
Is the Dies Irae sung?
Yes, and it's printed in the Orthodox Missal.