I have injected a Seam Renderer into a backing bean in order to generate an email from a template. The template itself is stored within a database, that is accessed via a custom Facelets ResourceResolver.
The resource resolver works, as web requests to URLs go through it and load the templates correctly.
OTOH, the Seam Renderer does not seem to hit the resource resolver at all. It appears that it only uses the default resource resolver.