I don;’t believe so – I THINK they are a fuller explanation of any particular topic. However, your precise question asks if they are examinable. To be technically correct, well, yes they are. Anything within the syllabus is examinable. The Kaplan exp texts simply expand the topic to give students a fuller / more complete understanding of the topic involved.
NB I have NOTHING to do with Kaplan, I am not related in any way, and I therefore am unable to give you a definitive answer to your question. If you want an official answer, I suggest you contact Kaplan direct.