I will confess to not getting this discussion. What is this about "believing in Ki or not believing in Ki"? I definitely don't get what is meant by "teaching Ki" or not.
That's like saying "I teach Water" in my style of Aikido. Or "That teacher doesn't beleive in Air". These are verbal appelations for symbolic referance to different types energies. These are not "things that are known or not known", you don't learn Ki nor do you teach Ki.
If you mean by this discussion that some teachers prefer to describe technique in terms of the physical principles of technique such as the geometry, balance points, principles of joint locking etc. and other teachers prefer to use the symbolic representation of the five elements and their myriad energetic combinations I would say that was true. Certainly there styles of Aikido which place emphasis on learning "Ki exercises". These are meant to develop the balanced flow of that type of energy in the body and enhance an awareness of that energy. You could even go so far as to say that Ki exercises can foster an awareness of the connection between the Ki of the individual and Universal Ki. But it is the exercises that are taught not the thing itself. "Belief" in Ki or "disbelief" in Ki is a misnomer.
That said there is a debate within Aikido circles over what emphasis should be placed on the element of Ki in the practice. One extreme would be Koichi Tohei Sensei's style of Aikido which goes so far as to grant separate ranking in technique and ki development. The other side of the coin would be represented by Kuroiwa Sensei who felt that too much emphasis on Ki made people neglect their understanding of the fundamentals of technique in favor of some "magical" energy which would make their technique work despite their lack of fundamentals.
The vast majority of Aikidoka fall somewhere in between these viewpoints and that includes Aikikai folks.