[John 19:19-22] And Pilate posted a sign on the cross that read, “Jesus of Nazareth, the King of the Jews.” The place where Jesus was crucified was near the city, and the sign was written in Hebrew, Latin, and Greek, so that many people could read it. Then the leading priests objected and said to Pilate, “Change it from ‘The King of the Jews’ to ‘He said, I am King of the Jews.’” Pilate replied, “No, what I have written, I have written.”
[Romans 10:9] — “If you openly declare that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved.”
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Pilate confessed with his mouth (and wrote it down in three languages!) that Jesus is Lord (”King”).
Pilate was of course alive during the resurrection, and present for all of the Jewish drama around the crucifixion. He was a participant in the activities around the resurrection.
I am able to believe that Pontius Pilate confessed that Jesus was LORD and believed in his heart — knew — that Christ was risen from the dead. And, therefore, saved, as Paul set out in his letter to the Romans.
That’s not a definition of “saved”. The demons no doubt believe that Christ is risen too.
Seems more likely it was meant to discourage rebellion. Recall some Jews wanted Jesus to use his influence to lead a rebellion against Rome.
One of the themes of the Bible is that God flips the script that is expected by us humans. It happens throughout the Bible so this would fit in with that theme. Pilate would be one of the most unlikely Christians ever but as Jesus said with God it is possible.