No, you CAN use Publish Website to publish to ANY server. The problem is trying to add it to a WordPress site. I can't visualise your idea, but is it possible to create a folder via FileZila and publish the Xara site to that? You would then link from the WordPress site to the Xara site and vice versa.
You could use the Publish Website option, changing the green section in the attached picture to the name of the folder you created.
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