No. It is not suicide in either the Western legal sense, the medical sense, or the Catholic doctrine.
Legally and medically, it is very well known and agreed that a patient has the right to refuse treatment at any time. IF you don't want a life-extending therapy, you are not required by law or ethics to keep it. The Catholic church recently cleared this up as well.
The key is understanding what is the causing the death. ALS is the killer. As we all know, the therapies and treatments--including masks, O2, food, water, morphine and anything else--are not going to change the final result, so they are simply to relieve suffering. It is permitted and encouraged to relieve suffering. But it is not required that a patient must keep himself alive at any cost. A terminal patient always has the right to refuse, withdraw, or stop any therapy--even if the result will be death.
The law and the church go even further, to talk about morphine. Morphine is a pain and panic reliever. OF course, we all know that, at a certain dosage, too much morphine is fatal. However, in the case of a terminally ill patient, remember that it is the ALS that is doing the killing. The nurse with the morphine is relieving the pain and panic. Therefore, it is acceptable--with a terminally ill patient--to continue increasing to whatever dose is required to relieve the pain and panic, even past the fatal dosage. The nurses intent is relief.
In the Assisted Suicide movement, they have made a mistake. It is NOT suicide. (Suicide is considered a bad thing, a choice between life and death. But with a terminally ill patient, there is no choice, so there is no suicide. The movement needs to call it what it is: Managing your own death experience.
References available upon request.