I heard Seam conversations are propagated through JSF POST request. Can I do redirect-after-post or even GET in the same conversation?
Yes, on both accounts! To use redirect-after-post, you just need to enable the SeamRedirectFilter in web.xml. To propagate a conversation through a GET request, pass the conversation id in a request parameter named conversationId. By default, GET (non-faces) requests always occur in a new conversation.