Both Nikon D800E and Nikon D810A have 36.0 MP resolution sensors but Nikon D800E's sensor is Full frame (35.9 x 24 mm ) and Nikon D810A's sensor is Full frame (35.9 x 24 mm ).
Since Nikon D810A's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Nikon D800E.
Another difference between these two cameras is that Nikon D800E's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the D800E and D810A sensor size comparison.
Nikon D800E and Nikon D810A have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.