Is this good for students who don't know any Japanese?

I'm assuming you are referring to the semester abroad program and not the summer program in my response since I can only speak about the semester abroad program.

To be short and succinct, no. The program adheres to a strict no English/only Japanese type policy which would obviously make it difficult if you don't know any Japanese. However, I will say that one of my classmates was indeed in your shoes (knew zero Japanese coming in) and he made it through so I suppose it's not impossible.

Short answer: yes.
Long answer: While it may be very difficult at the beginning due to the strict language pledge, it is for that same reason that I will eventually become very good for beginner students. Being forced to interact in Japanese from the get-go is a great incentive to learn basic communicative Japanese and really helps kickstart the learning process. So it may be a bit stressful or hard in the very beginning, once you get past that stage it is very good for beginners.

The CET Japan program is great for students of all different levels of Japanese proficiency. To specifically answer your question, I would say yes. This program offers an intensive language class that will excell your language abilities faster than you could even imagine. However, there will be times where it can seem like a lot; being in a new country and learning a new language. But the assistance from the CET Staff/Teachers and Japanese roommates are so helpful that I would not worry too much about it. Everyone is welcoming and very understanding of your abilities and only try to help you improve them. I would keep that in mind as you continue to think about applying for CET Japan.

I believe it is possible to get through the program without knowing any Japanese. The program can be overwhelming due to the language pledge and not being able to communicate effectively at first can be hard, even for people who've studied plenty of Japanese language but not gone to Japan before, but I know there was a student in my program (Fall 2019) who went in with no Japanese and passed the program, so it is possible to go in with no Japanese language skills and still enjoy what the program offers.