There are some similarities, but I think a lot of that could be coincidence, though. Several Pokemon share a couple stats or stat totals or move levels.
But most of all, Ken Sugimori said in an interview that Mienfoo and Mienshao were added in to the game late in development because they didn't think there were enough fighting-types. They hadn't done kung fu yet, and he remarked that most fighting-types looked human-like so he wanted to make an animal-like one. (Although I wouldn't say "most"...) So if they intended Mienshao to be a parallel, they only thought of it later, after Zoroark was most likely already developed. Also, he never mentioned a connection between the two in this interview, and they were mentioning all lot of stuff like that about what Pokemon were intended to be.
You're right about Fighting-types and Dark-types being opposites, though. Fighting represented fighting with honor and dignity, like a samurai. Dark represents fighting dirty, dishonorably, cheating. This is why a lot of Dark moves are things like Thief, Fake Tears, Faint Attack, Beat Up, and Sucker Punch (which is named Ambush in Japan.) This is why Dark-types are weak to Fighting-type moves. Honor trumps dishonor.
I'd be more inclined to think that if Zoroark had an opposite, it'd be Lucario. Both are the new class of "mascot Pokemon" that Game Freak has seemingly created (by which I mean those heavily-advertised Pokemon who aren't legendary, are one of the first to be revealed and star in a movie before the game comes out.) Also, Lucario can see hidden things and Zoroark hides thing. Zoroark creates illusions and Lucario has the power to see the truth.
Houndoom and Sharpedo are not opposites.Well...they are when it comes to typing but that's it but think Gyarados and Milotic
I think he was saying that Houndoom and Sharpedo are frail mixed attackers, not that they're opposites.