AFAIK neither Unreal nor Unity will frustum cull the triangles of a model out of the box and although both offer some other forms of occlusion culling they also only operate at the whole model level.
Occlusion culling in Unity is fairly straightforward. Simply requires a bake. It also supports 'occlusion areas' where you can give it a hint to do a higher resolution occlusion bake e.g. if you think the player will likely be in that area.
Edit: originally misread parent as stating Unity didn't frustum cull by default. Parent comment is correct.