Perhaps you mean a Content Type that you created? Because you do get to specify that.
Out of the box, there is the OnPublished event (I did not see an OnPublishing event. If you do, then please ignore the rest of this post :).
Handling the OnPublished event would be too late for you to cancel publication, so you would probably have to implement your own event that is triggered during the OnPublishing event ("contenthandler" event, not "rules" event). The OnPublishing
event receives a context that has a Cancel property that you can set to cancel the item from being published.
However, even when you do implement your own "OnPublishing" event and trigger that from your content handler, I don't think there's currently a way to inspect results from actions in order to set the Cancel property of the PublishContentContext.
Now I happen to know that Sebastien is working on some very cool workflow implementation that may replace the rules engine, which may support this kind of scenario without writing code, I don't know.
However, until then, you could implement a content handler in code that simply cancels the publication of the content item if your service call fails by handling the OnPublishing event.