Yes, there will be such complications, however using standard workflow in UE with fixed camera means he’ll probably be stuck using Lightmass and the effect he is looking for may not be achieved that way since ‘maybe’ depending on the style and level of detail he is looking for, a certain aesthetic would be better achieved with offline renderers or even a paint over after a render is done. To find a middle ground he could import the objects as they are in UE but use Offline renderer to bake everything in as texture, then use an unlit material on those objects in UE.
Another technique would be to use projection mapping (commonly used in VFX), this way he’ll retain depth as well.
Later match everything to that for the characters in the engine.