People have said SWG and JTL used seperate engines, I dunno how true that is.
However the newest versions of the Hero Engine do support "space"....... and frankly upgrading the whole game to that might solve a lot of other problems too.
If all they do is mildly take space off the rails then it's never going to be what most people want.
JTL client was the same as SWG client, so no, JTL was not developed for anothre engine.
But lest's say it could be another engine. The problem is not a question of graphics, is how the client negotiates data traffic with server side of the engine, so basically ground and space engines must be the same because they've got to understand and be undertood by the server side.
Use the later versions of Hero engine is no possible. BW adtimited that they have changed so much the version of their engine to the point is no longer compatible with any subsequent version.