For creating Zendesk tickets with Zapier, I think the best approach would be to point a Discourse Post Event webhook at a Zapier webhook trigger. This topic gives details about how to set that up: Discourse Webhooks and Zapier. The example that topic uses is for sending an email based on a User event, so you will need to set things up somewhat differently.
I haven’t tried creating Zendesk tickes via Zapier before, but it looks like it will be possible to do. Let us know if you have problems setting it up. One thing you will need to do when setting it up is add a filter step on Zapier so that the zap only creates a Zendesk ticket for the first post in each topic.