Yes, in the Platform Sutra we are told that Huineng was illiterate. Those who made up the story were obviously literate people, not to mention that the Platform Sutra itself warns people in chapter 10: "You must not revile the sutras, which is a transgression immeasurable." Also, considering that to become a monk one first had to pass examinations (it was imperial law for quite a few centuries), it was practically impossible for any monk to be totally unfamiliar with writing and some common Buddhist texts. Plus Zen was elite Buddhism in China and East Asia (few Westerners realise that those who have received dharma transmission and became recognised Zen teachers were abbots of monasteries, that's why the so called Zen monastic rules of Baizhang talk a lot about the abbot but there's little mention of any Zen master per se) that thrived in literary production, you just have to check out the number of Zen related texts in the Buddhist canon that exceeds the works of any other Buddhist school.
The Buddha has certainly told the simile of the raft. It means that once you're on the other shore you don't need the vehicle. However, it is nonsense to talk about letting go of the raft before we even have one. Here is a good example of completely misunderstanding both Zen and the simile.
Typically, the first koan given to the beginning student is based on the two views of gradual practice and learning versus direct perception that comes out of the Huineng incident.
For the record, Zen does not revile the scriptures, and I did not suggest "jettisoning" the teaching.
I will not be taking any further part in this discussion.