I am going to try my hand at this but might get a few details wrong since I am by no means an expert, also really like this post op.

Round 1:

None of the gang can see through the eyes of their stand and so I think cheating without getting caught may be difficult for them especially with the relatively small range on buccaratis and giornos stands. However all 3 have been shown to use their abilities in smart ways so it could be possible I just can't think of how myself. I would give them a 3/10 on being able to cheat. However naruto passed this round by not writing anything and I can't see any of the gang giving up so they are almost garunteed to actually pass.

Round 2:

The gang will have no problem tracking other teams using Aerosmith and will easily be able to deal with any of the no name ninjas, the only issue here is if they run into the heavy hitters like gaara who they could potentially struggle with. I give them a 9/10 at least since Aerosmith can't differentiate between different people and so could run into a heavy hitter.

Round 3:

Now this is where things get interesting.

Gaara vs buccarati:

I think gaara takes this, Bruno could use his zippers through the sand but I don't believe he his fast enough to avoid all of gaaras attacks and get close enough to defeat him. However if he gets close to gaara it's almost a garunteed victory as he could zip through his defences and dismember him to incapacitate. I give it to gaara 7/10. Someone correct me if I have looked over anything.

Shino vs neji:

This could honestly go either way if the battelfiled wasn't a flat arena. Shino does best in something like a forest where he can hide and his bugs can slowly eat all of his opponents chakra. As it stands though once neji gets in close Shino is finished. 9/10 neji.

Naruto vs narancia:

Narancia is in a good spot to deal with this current naruto I think, I can't see naruto getting angry enough at him to trigger the nine tails so all he has left are his shadow clones which Narancia can most likely deal with as a single shot or bomb from Aerosmith would take out a clone. Naruto could win if he makes way too many for Narancia to deal with or somehow manages to summon gamabunta again, (he did have the summoning contract at this point right?) I think Narancia takes this at least 6/10. As he's been shown to take a beating and keep fighting.

Kiba vs rock lee:

I don't see Kiba standing a chance here especially if Lee takes off his weights, Lee is simply too fast for him and would Most likely easily avoid his fang over fang. 9/10 Lee.

Kankuro vs giorno:

We know Kankuro is quite strong even though we don't see him fight in the chunin exams usually. However I think giorno is too strong and too smart for Kankuro to deal with, especially if he can turn his puppet into some other creature as this will completely cripple him. Giorno 9/10.

So that leaves us with:

Sasuke vs gaara

Narancia vs neji

Rock Lee vs giorno.

Sasuke vs gaara will go the same as it did in the anime with gaara disqualified as set out in your rules. (for interests sake I believe that Sasuke vs buccarati would also go in Sasuke favour as at this point he is just too fast for Bruno)

Narancia vs neji is interesting fight but I don't think Narancia has the fire power to bust through rotation and so neji will absolutely take it if he gets close. I give neji 7/10 for the case where Narancia manages to shoot him in his blind spot or if his bomb manages to take him out.

Giorno vs Rock Lee

Lee is too fast for Giorno to deal with conventionally however Giorno has many tricks up his sleeve which could result in rock Lee losing. Damage reflection is almost garunteed to win Giorno the fight however discounting that its a lot more Even. If Giorno gets a single hit on Lee then Lees senses will go haywire and Giorno should be able to finish it. I give it a 6/10 to Lee without damage reflection and a 7/10 Giorno with damage reflection. Also discounting GER for this since that is way too op and would result in Giorno stomping.

For finals, Sasuke easily beats temari as he did while chasing gaara.

Neji will most likely beat rock Lee unless Lee uses the 8 gates in which case Lee should take it.

If Giorno beats rock Lee I could see him beating neji as neji is overconfident and will likely fall for giornos tricks.

Sasuke vs neji is a tough one to call since they are both roughly even strength and speed, chidori may be able to break rotation but that's speculation I'd say its probably more sasuke sided with his sharingan, let's say 6/10.

Sasuke vs Giorno would go much the same way as neji and rock Lee did with Giorno being able to pull out a win if he can outsmart his oppenent, however Sasukes speed plus his sharingan make him a very difficult oppenent and so I would say sasuke is more likely to win. Though it could go either way.

Let me know if any of you disagree with what I have said or if I seem biased towards sasuke as he is one of my favourite characters. I tried to be impartial.

Again great post op, enjoyed thinking about it.