Different applications use different techniques to calculate the padding. If it looks a little different in the empty space this is unlikely to cause any problems. Generally, Eric's advice makes sense but the padding distance applies more to when the textures are viewed from a distance at lower mipmips. At mip 0 this…
I don't see seams on lowpoly mesh, it looks like that in Blender viewport for example: Maya and Blender have some smoothing settings for UVs, but in Zbrush I am not sure how can it be. For example I have a highpoly and lowpoly meshes, and I do "projectALL" LP on HP or just copy+paste UVs in UVmaster zplugin if necessary. I…