"Firstly, the bulk hydrogen loss was aeons ago. What we measure now is the deuterium ratio left behind, which is quite high. Thus it's reasonable to infer Venus once had a lot more light hydrogen combined with water."

Or Venus once had a lot more light hydrogen. Is it required that the Hydrogen was once water which was then split into H and O?

"Secondly, the solar wind has been observed blowing away Venus atmosphere, so back when it was losing bucket loads of hydrogen it would've been quite a plume. Now the hydrogen loss rate is much lower and most observed gas loss is broken bits of CO2.

Thirdly, there's nowhere to hide the ocean in the observed atmosphere. Venus really is very, very dry. There's probably not much left in the mantle or the rocks either, but that'll take a lot more work to quantify."

Currently Venus atmosphere is suppose to have around 20 ppm of H2O:
" Minor (ppm): Sulfur Dioxide (SO2) - 150; Argon (Ar) - 70; Water (H2O) - 20"
http://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html

So, .002 % of a Total mass of atmosphere of about 4.8 x 10^20 kgs
Or very roughly, .00002 times 4.8 x 10^20 kgs is
about 9 x 10^15 kgs of water or 9 trillons tonnes.
Or somewhere in the range of how much water Mars may have.
Granted 9 trillion tons is not what you would call a ocean, but if there actually is 2 or 3 times this amount in the Venus atmosphere which has not be detected, then it could add up to something you could call a small ocean.

And if you are splitting an ocean of water how much energy does this require, how much energy would available which could possible do this and how long would it take?

As a baseline, how much water which is emitted from comets is split?
Or if humans were to deliberately attempt to harness solar energy how much water could be split. Say, cover entire earth with solar panels and how long would it take if the sole purpose of the solar energy was to split all the water in the ocean.
And can we assume that humans could [if this was their sole purpose] be significantly more efficient at doing this, than compared to nature?