Unfortunately there is precious little that can be said on this, as we can't really know the deepest thoughts of a man's mind, and Zhukov certainly wasn't going to advertise his Orthodox faith if he had, in fact, retained it. You're certainly correct that a profession of faith would have at the very least prevented his advancement in the military and party in the way that he did, as I've written about here, so you'll find no evidence of it in his memoirs or other writings. As an infant, he was baptized, and in his memoirs makes some mention of church attendance, but with the enthusiasm you would expect of a young man just moved to the big city:

On Saturdays, Kuzma took us to vespers and on Sundays to matins and mass. On big holidays our master took us to mass at the Kremlin Assumption Cathedral, or sometimes to the big Cathedral of the Saviour. We did not like going to church, always looking for a chance to escape. Assumption Cathedral was an exception, of course, for there we enjoyed the glorious choir, and were especially eager to hear Deacon Rozov who had a voice like a trumpet.

Like a good Communist, he makes no mention beyond that even if it might have been the contrary, and in any case any active practice would have ended by the Civil War and his joining in with the Bolsheviks.

In his biography Stalin's General, Roberts notes that there were some small rumors, such as that Zhukov kept an icon in his staff car during the War, but it is only that, small rumor, as his driver denied it in his own memoir.

The only 'evidence' that we have for Zhukov retaining a real sense of Orthodox faith into adulthood comes from a fairly questionable source, his youngest daughter Maria. She has long been the custodian of his legacy, maintaining his papers and overseeing the publication of a number of Russian language editions of his memoirs after the fall of the Soviet Union (none of which are translated into English, sadly).

A few things are important to understand here. The first is that she was only born in 1957, to his second wife Galina Alexandrovna, and was 17 at the time of his death in 1974. She knew a very different man than even his other, older children would have, let alone anyone who knew him in the war. And more importantly, custodian is probably a light term, and it is more accurate to say jealous guardian, as she plays an active role in shaping the perception of him as a hero within the new post-Soviet landscape of Russian nationalism. If you check the footnote cited by Wikipedia, you'll note that it goes to an article written by her.

She makes the utterly unsubstantiated claim that, as translated by Roberts (and I believe from the same piece):

Father was by birth, upbringing and outlook an Orthodox person, just like his soldiers, who said with him before battle, ‘we go with God!’

There is absolutely nothing to support he maintained faith to this degree beyond her word, and much reason to doubt it. As noted in the answer I linked above, open profession of faith was allowable within the Red Army during the war, but it was an assured way to end your career both in the military and the party once military necessity was over with. Open practice such as what she describes is quite unbelievable. Rumors like that would have dogged him through the rest of his career, and the fact they didn't surface during his points of disfavor speaks volumes for how unsubstantiated they are.

To be sure, it is possible, even likely, that he retained a very rudimentary belief, as the same can be said for the majority of Russians of his generation during the Soviet period, but that doesn't mean we can ascribe any sort of active profession of it to him, as we lack any evidence beyond a very biased, and very unsubstantiated source. All evidence points to the fact that whatever beliefs he had in favor of religion, he kept very private, and tales to the contrary are a conscious rewriting to make him better fit the image of the hero in the post-Soviet landscape.