I don't see why tools which monitor application/hardware usage is good enough? Besides if they can developer AI which can detect malicious codes to hijack supercomputer, why limit it to cryptocurrency mining when there are other malicious things (such as stealing information or make server down).
Maybe this is just the first step to it? Maybe they are trying to teach their AIs to detect unusual behaviors that might help them develop an AI to prevent malicious things like you mentioned.
But if the hacker is smart enough, attacking supercomputer will be easier if it can't detect a malicious software, he can just set the mining to minimum and since the supercomputer can mine faster I think that would not be noticeable at all.
I agree. Even a small amount of computing power means profit to those hackers. Though this might be trivial to many, this is a huge step to computer experts to understand behaviors and AIs which might help them in future endeavors. Even small things can be useful.
Though some might disagree and say "they should have used their resources to other projects that is more important".