"Emissive" in this case is a technical term indicating the material is not affect by light sources in the scene. It just renderes the texture/color as it is. Because that makes it appear like it emits light, it is frequently uses to render meshes of a light source (e.g. some lamp or monitor), but it is not a lightsource it self. To affect the surounding objects, you still need to place a Point- or Spotlight. For example using an Invisible Light atom.
Realtime area lightsources are not supported by VaM, as the performance on dynamic objects like characters would be terrible. Basically it would need realtime raytracing. (Yes, yes....Unreal 5 Lumen can somewhat do this stuff now, but its limited and performance isn't quite good enough for VR and of course VaM is using Unity engine tech from 2018...)