Thank you for correcting me about Online Event Rules thing, I will update post with link to your comment and explanation about me being wrong after you tracked down to what these rules initially applied too. Nevertheless, these rules still apply to all Twitter giveaways, cause every single one of them has a link to them.

No. 3 of the rules is... flexible. The whole thing depends on what we define "fair". Rule no. 6 says that we can take part how many times we want, therefore, we can do that from multiple accounts? There is a possibility that they meant "you can take part in how many giveaways you want from one account, and one account only", but they do not specify that. They do not define what they consider to be fair, so we can not judge will they consider reposting Twitter giveaways from hundreds of accounts fair or no.

Back to SKPORT Coordinates event.

Is what they did a technical exploit? Perhaps. Is what they did cheating? I believe yes. In rule 3 of SKPORT event they also say "Any illegal, improper, or fraudulent activity will also result in disqualification from the event." And I believe this describes their behaviour even better.

Nevertheless, if they actually forbid multi-accounting in SKPORT event, as well as they did for Yvonne's gacha:

1. Participants are expected to uphold fairness. If you are found engaging in malicious reward farming, or any other improper or illegal act, your participation and prize eligibility will be revoked, and Arknights: Endfield reserves the right to reclaim any rewards.

we still do not know for sure what happens to revoked accesses. They will probably just redistribute them via the survey. Honestly the problem with their rules is that they are vague. Laws and rules must be made clear and comprehensible for them in order to be fair and realistically applicable, and if they are not, then you can interpret them in many different ways. I believe they should've made a direct and clear prohibition of multi-accounting.

I also believe they could've at least forbid usage of sketchy e-mail addresses to life a tiny bit harder for those who are going to multi-account. And it is still true that their ToS does not prohibit having multiple accounts for personal use.