Revelation references no sources; in fact, it claims to have all its information from mystical visions, not any objective evidence at all. Someone, in other words, just dreamed all this (or was claiming to). And so far as we know it had no sources, other than “The Gospel according to Matthew,” which was simply an expanded redaction of the “Gospel according to Mark.” Revelation is therefore derivative and thus cannot corroborate anything. All it does is prove Matthew’s historicism existed at that time. Which we already know—from Matthew (and Mark, whose text is even earlier). It therefore can have no effect on the probability of historicity. Once the Gospels exist, it is already 100% expected there will exist texts expanding and riffing on them, like this, regardless of whether Jesus existed or not. So we are back to simply assessing the probability of the Gospels.
Nevertheless, Revelation is actually a little cagey about whether historicity is actually true, rather than symbolically represented. In Rev. 11 it sufficiently implies Jesus was crucified in Jerusalem; but in Rev. 12, Jesus is born in a lower heaven (in the vicinity of the moon), and soon whisked away to even higher levels of heaven, and seems never to leave there (in a manner that fits the Star Gospel that in OHJ I find in Ignatius and the Ascension of Isaiah). So it’s unclear which version of events the author believed actual and which merely allegorical. It could be both, depending on one’s level of initiation at the time, just as was the case for Osiris cult.
But regardless, since the author shows no sign of having any sources of information other than the Gospels we already know about, and his own imagination, it doesn’t matter. We can’t use it to prove anything in the Gospels is true. We can only use it to prove they were circulating by then, which we already knew, and thus already accounted for.
I confess that this answer is not so satisfying, since the idea that Revelation is based on Matthew seems improbable to me. So I think that the best defense of the Outer Space theory is still made by Paul-Louis Chouchoud, with his condition that in Revelation the Lamb is killed before the same foundation of the world. Now I understand better why Robert M. Price insists on that point: he has understood that Revelation dates to 70 and is pre-Gospel, differently from Carrier.
It is hard to think that the Christians hated the Roman empire only during the time Revelation was written. The hostility had to be there even before, and even more intense.