For anyone wondering if Threads and Facebook at large will be a fine neighbor in the space and compatible with other apps/services in the fediverse: they’re already automatically hiding comments that mention Pixelfed https://mastodon.social/@dansup/112126250737482807
Unfortunately there is no explicit list, but I believe there are tools that will draw a graph of the fediverse and allow you to check that a particular instance does not. I’m not sure what the name is off the top of my head.
Naturally, if you see anything posted direct from Threads in your feed, that means your instance that you’re connected to is passing that data.