I once heard from a classicist friend that Vergil, the epic poet and miracle worker, was treated very much like a saint in the Catholic church, hence his appearance in the mosaics of a famous cathedral in Siena(I think?) and his role in the Divine Comedy. I have not found any good information online, however.
More importantly, though, some Greek Orthodox websites list feast days (and therefore name days) for clearly pagan names, like Herakles, Perikles, Themistokles, Sokrates, etc. Now, I'm very aware that many gods and heroes were slowly given "Christianized" names and identities after the fall of Rome, but the idea of putting these figures in their Classical names on the same level as saints is rather odd.
My question for you is are there any Christian saintly or saint-like characters from before the time of Christ?
Are they clearly Pagan names? When you meet a guy named David, Samuel, or Isaiah is it safe to assume that they are Jewish or Christian? For instance, Socrates Scholasticus or Socrates of Constantinople was a 5th century AD, church historian.
Though Saint Paul and other early sources show some Platonic influence, it is not until Origen in the early 3rd century that a major source arises for syncretism between Platonic philosophical precepts and Christian theology. The existing philosophical schools in places like Antioch provided a model for how Christian thinking and teaching would take place, and even is a factor in the development of monasticism. In many places Christian thinking just took over these ready made schools that had seen and entertained many systems and "schools of thought" from Platonism to Stoicism.
Augustine read Plato and Cicero and was deeply influenced by them both. Seeing as they both preceded the coming of Christ on earth it would be unreasonable to dismiss them outright because they were not Christians. This is what happens with Virgil as well. Origen, and later Augustine, both sort of "baptised" Plato's thought. Those adjudged to be teaching wisdom, purpose, and virtue in keeping with Christian ideals were praised. If Christians believe their God is eternal and the source of all truth, then it follows that any truth or wisdom in earlier writers would be evidence of God's provenance and providence, a sort of pagan, intellectual prophecy, if you will.
The Christians did not believe that Jesus altered morality (especially since the belief would be that He is its origin), but rather he provided a salvific means of atonement and taking on His likeness in goodness, perfection, and love. So because Aeneas practiced familial loyalty, or Lucretia chastity, or any other mythic character some virtue before Christ does not mean that what they did was not virtuous.
So to answer your question, no there aren't any "saints" that were not Christians, but the virtuous acts and thoughts that were in accord with later Christian ideals, earned many pagans the status of the "Virtuous Pagan" in Dante and in others.