I think I have sat back and read about enough on this matter.
By principle, if every attack is easily dodgeable, then this free for all would go on forever, unless you're like Kamui and forget an attack or two, in which case it would probably still take awhile for this to conclude.
Claiming to use an "undodgable/unavoidable/unblockable" attack
Undetectable is not included, so technically using an attack that is either extremely fast or not detectable is the only way for any of you to catch each other off guard. Dato's post stated:
The only real way he would have known about the attack is when it hit and then his torso would be gone.
The Kamui process is: activation, barrier forms, space-time ninjutsu magic sucks in or spits out stuff, Kamui is deactivated, space-time ninjutsu magic ceases, and then barrier dissipates. Dato's claim is that this happens in half a second, an incredibly small interval of time to react even by SL standards.
I searched the discussion thread for the rules, and unfortunately, not much context is given under which said rule was made, and so only what is written is what I have to reliably go by. The attack is not, generally speaking, unavoidable (as in, with a certain combination of things it can be countered) as has already been professed in this thread even by the technique user. He is not claiming his attack to be unavoidable. An individual who can react at the microsecond level and have certain methods can dodge this attack.
Equally important though is that Dato does not unleash his Kamui attack until after Athos launches his attack and Dato dodges. Now, while the dust release may travel however fast, to assume that Athos simply falls towards the ground after seeing that his attack on Dato failed (because yes, he would be able to detect that Dat pursued him at least up until he leaves the clouds, so he is not ignorant to Dato's presence) is not reasonable, giving more time for Athos to react.
The question then, is what does he do with this time? Well, as a zoner, that is up for him to decide at this point. If he wants to argue that the double Kamui is not possible then that is a logical next step. If he wants to argue that Dato should be skewered due to inadeuate dodging, then by all means. As the judge though, I rule that the attack does not violate the Competition rules.
TlDrNeither of their attacks violate the rules as far as I am concerned.
What's next on the docket?