You will want to stay away from 5.3 for now as it will be closely monitored since it's new content. I have already finished the first 2 quests using OHKO and no messages or bans so far. However I did it quite sporadically. I also have a really high account and have spent good money on it. I will likely go through 5.3 for completion, and I will only use Enemy Don't Block on the last quest. Hopefully, I don't raise some red flags.
Arenas are safe with OHKO. However, I'd be wary to use them on AQ/AW. For the safest bet, use Enemy Don't Block although it can be tricky to bait Specials then you find yourself eating a Special 3. All good though since you will not raise any suspicion from Alliance mates and the other team since you're taking damage. Having a power control champ works great in this regard.
Obviously this is for the VIP hack but since we're having the evading ban discussion here, might as well do it here.