The rough definition of a wormhole is a distortion in space-time that connects 2 points in space with a quicker route than that accessible through normal space-time. By this definition the Freespace subspace passages would fit into this fine, contrary to previous beliefs. It also would apply to space that has been folded in such a way as to make 2 seperate points convergent. Currently wormholes are believed to be created by intense gravitational distortions, such as those experienced inside a black hole (note: not every black hole would make a suitable wormhole in this case).
Enough ramble from me, here's a link to some discussion about the existance of real wormholes:
http://www.sciam.com/askexpert/physics/physics34.htmlStryke 9: I noticed that comment about having the ESS using a momentary shift. Working on that, if you could make the transitions fast enough (more of a vibration than a single conversion) then it would be reasonable to have the ship, plus drive, reactor etc simultaneously existing as matter and energy property-wise. This would mean that while it could travel distances very quickly, it would also have a solid foundation for the engine to actually keep converting the matter to energy and vice versa without irrevocably disappearing into energy itself. Of course, it would be power intensive, limiting the distance that you could travel in a single flight session (limit it to the same distance that it would fly normally with a single conversion, possibly extend it further), but this sounds like it could be a reasonable explanation/workaround of what you might be trying to achieve.