If i understood correctly, you need to combine 2 textures from 2 UVs to 1 texture and 1 UV ? You can do that in Modo/Max/Maya easily. Load 2 objects, create new UV (lets call it UV_combined), copy UVs from both meshes to that UV, pack UV (it rearanges UV so there is no overlap and keeps size of uv islands relative to mesh size). "Bake" 2 textures to new texture with UV_bake selected as target UV.
Admir