I don't think correct training in Sanchin kata is dangerous as long as the practitioner does not hold his/her breath. I think that when you are told to place the tip of your tongue against the roof of the mouth and to make the breathing audible it is actually to ensure that the glottis is not closed and so the valsalva manoeuvre is avoided.
It is instructive to be aware of Bill Starr's comments on page 5 of his excellent work The Strongest Shall Survive (1978, but republished recently I think) where he discusses the dangers of the valsalva manoeuvre in relation to performing a maximum lift.
Yours,
Harry Cook