I took Tarantulas' statement "(we) are from a different origin" to suggest that they weren't Cybertronian at alll... because if they were just reformated cybertronians by Unicron, they would still be affected by any temporal changes on ancient earth... unless you're saying that they were reformatted before the Beast Wars occurred thousands of years ago?
Either way, if they were created by Unicron or just reformatted cybertronians, I'd be guessing that they could have been "uploaded" with what Unicron knows, and he'd be expected to know about just about everything, including the Vok. (which allowed Tarantulas to recognise them, not by his own experience, but through his shared memories from Unicron)

Although, your version makes for a more interesting back story... which is always better for padding out a story with more depth than just the present.