Necessary in the philosophical sense? Must it have been Judas Iscariot and no other? No, I do not believe so. Any one of us could have done exactly what Judas did if placed in the same circumstances. To say otherwise is the height of hubris. We are all sinners. And all of us, in some degree, have betrayed God.

But I absolutely believe the role Judas played was necessary. With perfect foreknowledge of what Judas would do, Jesus chose him, taught him, walked with him, trusted him, broke bread and drank with him -- in other words, loved him. Christians are called to imitate that love, even to those who betray us. So I absolutely think it was necessary for us to see the relationship between Jesus and Judas.

As to your question - How would Judas work into the beliefs of Christian Universalism? - I would say, perfectly. 

Scripture says God will reconcile the whole cosmos to himself through Jesus Christ. Judas is part of the cosmos.That means Judas will be reconciled. The logic is impeccable. (If you haven’t visited our Universalism in Scripture page, I strongly encourage you to do so. Pay particular attention to John 12:32, Romans 11:36, 1 Corinthians 15:28, Ephesians 1:7-10, and Colossians 1:19-20)

But we need not think of Judas’ future reconciliation in such abstract terms. The beginning of his salvation is recorded in The Gospel of Matthew. Read Matthew 27:3-4 carefully:

Then when Judas, his betrayer, saw that Jesus was condemned, he changed his mind and brought back the thirty pieces of silver to the chief priests and the elders, saying, “I have sinned by betraying innocent blood.” 

Notice Judas “changed his mind”. In the Greek, it literally says Judas repented. Notice also he returned the silver. His repentance was genuine -- more than mere feeling, backed up with action. And finally, notice Judas confessed his sin. Confession, along with repentance, is yet another element of salvation (1 John 1:9, James 5:16). So with these verses in mind, we can feel confident Judas will eventually be reconciled to the Father.

Judas’ name means “God is praised.” Many Christians believe Judas will forever be excluded from God, and they praise God because of that exclusion. I believe the opposite is true. I believe all of us will praise God precisely because Judas was made fit to be included. I believe one day Judas will live up to his name and praise God with the rest of us.