Elgg does integrate with Wordpress to the extent that you can import your content. Eventually the plan is to have a fully modular system where you could swap out the Elgg blog and swap in Wordpress or something, but that won't be ready for a while - and will also require some extra (albeit generalised) integration support from the Wordpress end.

Incidentally, there are also a growing number of full-time Elgg users, including a number of universities using it across campus. One of our issues has been recording that, given that it's a free product that anyone can download without giving us any feedback.