Depends on the type of integration. 
I don't think it would be a good idea to post Discourse postings (or even links to them) to Slack or Discord. I'm quite sure many people would find this quite "spammy", especially if they already read the Racket Discourse. If someone wants to get notified about new Discourse postings outside of Discourse they can configure the email settings, which is completely opt-in.
Regarding the second type of integration, posting Slack threads to Discourse, I'm also somewhat skeptical. For one, I guess it might again feel spammy. Another issue is that a Slack thread often doesn't contain all the messages on the thread subject. In other words, some people post their replies to the channel and not to the thread. That said, I'm more open to this kind of integration as long as it's used sparingly, but I don't know how it would actually feel in practice.
This is just my opinion, of course. I'd be interested in hearing others' opinions. 
Stefan
Yes, I think I agree with Stefan; I want to keep the noise level down, I can barely manage as it is.