Any hacked item has the risk of being 'glitchy', and are completely unpredictable in what they do. Honestly, if you even see these items, leave as soon as possible.
Yeah, it's primarily the issue that you don't know under what means these items have been spawned in-game. Malicious intent, accidentally setting a value too high, or genuinely safe? You have no idea. It's very risky. The time to safely obtain these items will soon come, and it'll be a safe and fun time!
Also, don't accept wrapped presents from people; some hackers wrap lost items that can't be removed from your inventory.
Can someone explained how the hacked items can corrupt your save file? I cataloged them from someone for free not knowing they were hacked, but they appear just to be regular items that show up in your catalog?
I usually play the game in real time, but I had so much trouble getting the fall DIYs, that when I saw someone tweet they were letting people come catalog the Christmas stuff, it seemed much more convenient to just get it now than deal with the rng or color locking later.
From someone who has extensively read GBAtemp forums from the people who directly edit their saves, or just add stuff to their inventories, there has been no solid evidence as of yet. There was one **Facebook post from someone who received star frag trees, but it was soon removed; also still very unclear as to what actually happened. I transferred over wedding items to my unhacked Switch Lite before the event was unlocked, and everything was fine. *I hosted weddings on my island. My friends kept their outfits. Everything has been fine. You can't trust just anyone who will intentionally make items fritz out, because they might also try to give you stuff that will stay in your inventory forever. Thankfully though, there isn't anything worse, and no one (at least on the major forum for save editing n stuff) is working towards making destructive items and tools. It is beyond discouraged. I don't even know of anything game-breaking that happened in New Leaf...
Cataloging things is all good. Nintendo can't detect that items from your catalog were cataloged from hacked items.
EDIT: Also important to state: I am in no way condoning any hacking-related trading on here. I am not and will never offer or provide anyone items that have been transferred from my other Switch. Just wanted to make that clear!