True, though I've always been of the opinion that this was more related to the various teaching techniques, the influences that came to shape the understanding of particular teachers as they began over-shadowing doctrinal substance of the Ch'an tradition.
This is an excerpt from The Building Blocks of Chan Buddhism:
The general principles of Buddhism are evident in Chan Buddhism. That is to say that the world is an illusion conjured up by each individual's mind, that every thought has the power to produce a retributive future result (known as karma), and that it is this that decides what form we will appear in during our next life. Enlightenment occurs when we understand this, and nirvana is attained when we are emancipated from the endless cycle of life and death to join the Universal Mind.
Well, these are general principles upheld by some Buddhist schools, at least.
The main Chinese variations within Chan Buddhism are as follows:
1) The Theory of the double truth:
This defines two different kinds of truth, a common one and a higher one, on three different levels. At the heart of this complex theory is an examination of the inter-relationship between existence and non-existence. Truth is complicated by the fact that on the one hand there is physical form or existence and, on the other, everything is said to be illusory or non-existent. In which case, what and where is truth - within existence or non-existence? After considering this, the theory then considers the same question for enlightenment.
The theory of two truths heralds from Indian Buddhism, around the time of the Abhidharmikas, as hinted at in the early sutras.
2) "A good deed entails no retribution". This idea stems from the Daoist belief in non-action, i.e. that action without effort, which is natural and spontaneous to the essence of the individual, does not entail any future retribution or " karma ".
Chan does not make such a claim. Note in particular the "fox spirit" story, which clearly affirms the validity of cause and effect. Once the mind is purified, then karma is not created. Standard Buddhism, and no need to refer to Daoism at all.
3) The method of attaining enlightenment is to do things without deliberate effort and purpose and live naturally. This (again linked to Daoism ) prepares the mind for enlightenment.
Rather a vague statement, but most Buddhist schools have the idea of "kriya", actions which are not karmic, ie. act without intention. No need to refer to Daoism again.
4) That enlightenment occurs suddenly. Although non-action or living the life of non-cultivation diminishes distracting elements and facilitates contemplation, enlightenment itself is not a gradual process but a sudden revelation.
Well, the gradual sudden dispute is rather complex, and split caused by Shenhui and others really polarizes things excessively.
5) Although words can be a useful tool to explain a thought, they can only ever be an approximation to the idea. Thus, the state of enlightenment can never be described.
As described also by the Yogacarins, the Madhyamakas, a number of other early Indian schools, too. (See for instance, Nanananda's Concept and Reality.) So, nothing particularly Chinese about all this.
6) There is no other reality than this phenomenal world. Whereas the unenlightened only see the physical objects around them, the enlightened in addition to this see the Buddha nature within the phenomenal world.
Depending on what interpretation of Buddha Nature one takes, this is also accepted by a number of Indian systems. Buddha nature aside, a number of Indian systems also posited that reality, as nirvana, is also not another distinct dharma apart from the conditioned. Nothing specifically Chinese here.