Terragen 2 does have a LWO exporter so you can import that geometry into Vue. Also you can import a terrain heightfield from Terragen 2 into World Machine and or GeoControl and save out as a 16bit grey scale map and import that map into Vue's function node while in the terrain editor. If you have access to GeoControl there are options to save as a 16bit .tga, and a .obj format.
Terragen 2 has a convert procedural terrain to heightfield terrain node i believe?
I am a Vue user myself as well and the only reason why is 2 really, speed and spherical panorama rendering otherwise i would go back to Terragen 2 right now but i will wait for now.