(spoilers: I'm gonna be name-dropping some Stands and Stand abilities from Part 6-7)
No, there are no loopholes. No hidden tactics, technicalities or rules regarding Requiem that you can exploit. Aside from the non-canon The World Over Heaven, Gold Experience Requiem is the strongest Stand in the entire series, beating out Tusk ACT 4, D4C:LT, Bohemian Rhapsody, Made in Heaven, you name it. Here's why:
Gold Experience Requiem's ability isn't time reversal. It's not attack-based, it doesn't require conscious thought, and you can be damn sure there's no way to blitz it. It's nullification, quite simply. If something happens that Giorno wouldn't want to happen, Requiem says "no" and it doesn't happen. If you use your Stand ability to try and circumvent its power, say if Rohan tried to make himself immune to it or if Bohemian Rhapsody tried to summon a character who could defeat it, it won't work. You can stop time all you want, you can steal as many Stands as you want, you can reset the universe as many times as you want; nothing will ever work, period. Johnny activates ACT 4? No, he didn't. Johnny never even got on his horse and the Infinite Spin was never channeled. Valentine tries to send away Giorno's attacks? Nope, Requiem steps in and says he never got the Corpse Parts in the first place. There is no 'time limit' as to how far back its nullification can go, hell it's shown that it can even reset life and death itself. Giorno could just say that the action of you living never happened, which is literally what he does to Diavolo. The following is a list of bulletpoints. This is my evidence.
Point one: Requiem, and by extension its ability, Return to Zero, transcend time itself and will continue to exist and take effect in a pocket where time does not (i.e King Crimson). It's shown in the Risotto vs. Doppio fight that nothing except Diavolo exists in erased time, meaning physical objects become intangible if they are fated to move in that duration. On top of that, Requiem outright contradicts Epitaph's prediction, meaning that it isn't bound to fate itself, unlike Made in Heaven. All this points towards the fact that Requiem is not 'wrangled' by any higher power, not time, space, fate or anything of the sort.
Now, for point two: the infinite death loop does not require that Giorno kill the target for it to take effect. Remember, Trish says that she can still sense Diavolo long after he was put into his death loop, and it's never shown that Requiem's blows were particularly lethal. Going by how Gold Experience's original ability required physical contact with a target to function, we can deduce that the only thing required to place a target in a death loop is simply striking them. This is confirmed in its stat page. Avert your eyes to the following, ladies and gentlemen:
So, how exactly does it do such a thing? If Trish could still sense Diavolo, then that means he couldn't have been physically transported anywhere. That's where another teeny-tiny detail comes into play: Gold Experience Requiem creates a fucking pocket dimension to inflict eternal suffering upon you. The deaths Diavolo experienced were clearly 'fake', as all of them were rigged in order to ensure he would die, meaning that it wasn't just sending him on a cross-country trip into convenient situations where he'd just happen to die. He couldn't summon King Crimson to punch away incoming traffic or erase time to make himself invulnerable briefly, which, on top of that means that it disarms the target of any abilities that could potentially enable them to escape the death loop. Yeah, you won't be getting out anytime soon.
Lastly, point numero tres, and arguably the most absurd implication that Requiem's power has to offer: a lot of things constitute actions. Eating, walking, seeing, breathing, and even thinking. I've pondered over what Requiem meant when it said that even Giorno didn't know the full extent of its power. Action nullification is pretty simple, isn't it? Something happens, except it doesn't. And that's when it hit me: it's not just that. The act of existing is an action. That's right, I believe that Gold Experience Requiem has the power to erase you from fucking existence. Or, if it wants to, it could just nullify every action you've ever done in your life, every thought you've ever thought, every influence you've had on another person's life. And then, to make sure those actions will never happen ever again, all it has to do is kill you. No, this isn't a stretch. By sheer virtue of a technicality, Gold Experience Requiem quite possibly may have the power to remove anything Giorno wouldn't want from this world. It's just unfortunate that we'll never get to see it again.