As others have said, it doesn't cause corruption, but a lot of the pre-mades are corrupt. I think many players have thought of the concept of "corrupt data" as some sort of digital cancer. But it's best understood as simply unreadable or inaccessible data, which can either be partial or full. I think over the years the hysteria has come from people misunderstanding corruption, conflated with the general brokenness of the pre-made neighbourhoods.

Pleasantview and Veronaville were (re)created closer to the game's launch, so most of their problems are just developer mistakes/oversights. Strangetown on the other hand has every Sim with outright corrupted or missing data, which is why things often go sideways in this hood pretty quickly. Strangetown seems to have been created with a much older build of the game, so I suspect the cause is that certain data formats were changed during development. The dead Sims in Olive's garden are more affected than most, which is why they are problematic when resurrected. Yes, adding in readable data using SimPE is the fix for this. I'm not sure that every aspect of a character file is exposed in SimPE though, since certain sims (e.g. Knut Futa) still exhibit weird quirks even when replacing their data, so it's something to bear in mind.

Corrupt character data won't spread around the entire game like a cancer, but when the game can't find the data it's looking for, one of about four things is probably going to happen:
1. It will cause an error. The game has an error-handling function, so this isn't serious. It is possible though to be endlessly bombarded with error prompts if a Sim loaded on the lot is missing something critical (like Knut Futa missing, oh, you know, everything), making the game literally unplayable.
2. The game will read a corrupted value as a completely different (incorrect) one, which can cause unexpected behaviour.
3. The game will point to "random" data. This can cause problems if the game points to something unusual and unexpected for a particular function (e.g. daddy doggy). Other times it's just cosmetic, but undesirable (e.g. stolen faces).
4. For a few critical functions, the game will fallback to default values in place of missing data. These may not be expected values (e.g. Knut being treated as a baby).
It becomes a big problem if this happens with a lot of Sims in the hood, because the scale of it makes it difficult to manually fix things.

You can experience a cascading effect if the busted data is passed amongst Sims, though its impact is often predictable: A broken face can be passed down to children, who in turn can procreate with other Sims and pass on their broken features. But it's just a visual problem. It's not at all desirable, but it's not going to suddenly affect unrelated Sims and cause their faces to explode, or anything like that. It's also totally fixable, though if a lot of Sims are affected, it makes the task of doing so more arduous. Corrupt memories can be passed around as gossip, which on their own are usually unproblematic and easily managed. Though I've had the very rare misfortune once of having the NGBH becoming corrupted, which killed the hood completely (turns out it's an essential resource for a neighbourhood to function at all ).

I've got to wonder, though. Has anyone ever made fixed, downloadable versions of deceased Sims with broken/missing data? It would be so cool to have Olive's husbands living around Strangetown in an earlier timeline, for example, while keeping them as close to the real ones as possible. I think Strangetown Bella has some messed up data as well and I've seen fixed versions so I'm guessing it's possible?

Also... what exactly is the issue with the Tricous? I could've sworn people thought at one point that they were dangerous but now I'm not so sure. Maybe it's the subhood thing like with the Ottomai?