Every tutorial I’ve found on making material-based vertex animation uses some form of UVs. Is there a way to deform verts with a noise in world-space, so UV seams don’t tear?
Yes, use the material system’s “World Position Offset” input. This is a worldspace 3D offset that is applied to each vertex of a mesh. (Most material inputs contribute to a pixel shader for the material, but this one contributes to a vertex shader). See https://docs.unrealengine.com/latest/INT/Engine/Rendering/Materials/Functions/Reference/WorldPositionOffset/index.html.