The Greek word used in Hebrews 6:4 is φωτισθέντας which is pronounced "phōtisthentas." This word looks nothing like the Greek word for "baptize"-βαπτίζω. I cannot address if the Syriac words for "enlightenment" and "baptism" look alike and would be likely to cause confusion.
What I do know is that textual criticism, the art/science of determining the original text based on copies, operates on the principle that, all other things being equal, a copy is more likely to remove ambiguity and difficulties than it is to introduce them. Hebrews 6:2 mentions baptism (some translations of the Peshitta use the word "ablution" but that means the same thing) in connection with the basic teachings of the church. I can see a Syriac translator/copyist attempting to make things more clear because the question comes "what does it mean to be enlightened?"
However, the author of Hebrews answers that question for us in Hebrews 10. "Enlightened" appears in Hebrews 10:32 where it parallels the statement of 10:26.
10:26 For if we deliberately keep on sinning after receiving the knowledge of the truth, no further sacrifice for sins is left for us, 27 but only a certain fearful expectation of judgment and a fury of fire that will consume God’s enemies. 28 Someone who rejected the law of Moses was put to death without mercy on the testimony of two or three witnesses. 29 How much greater punishment do you think that person deserves who has contempt for the Son of God, and profanes the blood of the covenant that made him holy, and insults the Spirit of grace? 30 For we know the one who said, “Vengeance is mine, I will repay,” and again, “The Lord will judge his people.” 31 It is a terrifying thing to fall into the hands of the living God.
10:32 But remember the former days when you endured a harsh conflict of suffering after you were enlightened.
This also parallels with Hebrews 6. Hebrews 10 teaches that after receiving the knowledge of truth (which is enlightenment), if we deliberately continue in sin, there is no sacrifice for us. Hebrews 6 says that those who have been enlightened and then commit apostasy cannot renew their repentance.
In fact, in some parts of the ancient church, "illumination" was a synonym for "baptism." The connection most likely comes from these two verses (Hebrew 6:2 and 6:4). However, it was recognized that having baptism did not mean that one had enlightenment. John Chrysostom said, "Heretics have baptism, not illumination: they are baptized in body, but not enlightened in soul: as Simon Magus was baptized, but not illuminated."
In conclusion, I take "enlightenment" as the original wording in Hebrew 6:4 based on the parallel teaching in Hebrews 10:26.