I'm a strong advocate of believe what you want to believe, but there is no definite answer to this question so "yes of course they are (aren't)" kind of replies are baseless and add nothing.
Lucasfilm has the stance that during the Empire (and its rise) Clones are mixed with recruited sentients to fill the Stormtrooper ranks. This is basically a way of them taking the implied notion that they're Clones by Lucas himself and the Expanded Universe that, for decades, de-cloned the Imperial army and said they were recruited individuals.
That's LFL's stance, but not canon... Just a nice way to simplify an unanswerable argument/debate. Their stance says the Clones are from a variety of hosts that aren't all the swiftest in military expertise either, but rather picked for their political ties... This, to me, is total bull**** because I think the whole concept of ST's being "bad shots" and inept soldiers is pretty much a falacy. ST's mop up the floor with Rebel Soldiers on Hoth, Endor, and aboard the Tantive IV. Kenobi himself says the shots on the Crawler were too accurate for anyone but ST's (I don't view him as trying to sway anyone, he's merely pointing out what he sees as a fact).
ST's just can't hit Han, Luke, Leia, etc. because well it'd be a hell of a hard story to tell if all the characters died off quickly. It's like playing a video game with the utmost in realistic settings. If you tried playing Medal of Honor as if it were a real game, you'd not get off the beach during the D-Day landings because in real life you die... Or you're lucky and live. In Star Wars the heroes live because they have to so the story can be told, not because Stormtroopers are inaccurate Degenerated DNA soldier rejects. That's just people not being capable of thinking outside the box IMO.
That's LFL's thing. Others think that all Stormtroopers are Clones and they choose to disevow all the EU that says otherwise. I actually think Lucas himself feels this way but he never clearly states it in the films for one reason or another. He is known for wanting to contradict EU at times but being "persuaded" not to do so... He supposedly didn't want to use Coruscant as the planet's name since Zahn created it, but he was "persuaded" to do so by people within LFL.... Fine. Lucas isn't the end-all-be-all answer to anything Star Wars really if you choose NOT to listen to him. That's simply your way of viewing his art, and he can't sway you one way or another. It'd be like Michelangelo appearing while you mull over his statue of David and telling you WHAT to see instead of your mind telling you what you see. We had a lotta conversation about this very concept in my Tolkien Studies course as we read Lord of the Rings.
Other people believe Stormies are all recruits... At present that's my take because recruitment/training is a much faster means of building an army since Cloning took 10 years for them to mature to a fighting age, and ultimately I just like thinking that the galaxy was READY for an Empire. That the majority in the galaxy were so dejected with political affairs under the Republic, that people were so anti-alien/pro-Palpatine, that people were so ready for law/order and peace (remember, it's preached in E3, and a focal point of WHY the Empire is good), that they welcome the Empire with wide open arms...
Is everyone happy? No, but in the grand scheme of things the vast majority I believe are, there's lots of positives the Empire offers, and the Empire manages to hide the things it does that aren't so nice for quite a while... Or people are just as happy they did them. I mean if there's a lot of anti-alien sentiment, does anyone care if aliens are enslaved? Some planets will, but the Empire could be made of a majority who look down on the Wookiee Species for helping the Jedi who many perceive as trying to overthrow the Republic and take control via the confusion of the Clone Wars... People are taught to hate/fear the Jedi's, and that a lot of their plight in life is from their kind.
Anyway, that's just some of MY perspective but it's still not canon by any means... Canon's just what's in the films and undisputable by other sources as far as argument goes. But how you view the films, the EU, and all other facets of the Star Wars galaxy is personal interpretation, and with that there are no "rules" to live by... Canon included. It just makes no sense to come into a discussion about the SW galaxy though and say, "yeah well I don't believe that even if it was in the film so your point doesn't matter". That's fine to feel that way, but it doesn't make for good discussion/argument.
I'm to the point I could buy the LFL stance of Recruits mixed with Clones (I don't buy the various host theory though and I'd envision ALL Clones being Jango Clones, till the clones in Zahn's trilogy but that's another topic). That's a nice way of accepting the film's implications and the EU all in one nice neat package. Right now though I'm still leaning towards ALL recruits in the Empire though. It adds a vastness to the galaxy that I love too... That they could recruit that many possibly Trillions (or even more?) people into their military juggernaught. That's practically impossible to even fathom for me, but that adds so much to Star Wars for me too.