The rumors aren't the only thing keeping him from being a top-5 prospect. His slow feet, that he doesn't seem to care to improve, keep him from being in that class. And, it's not something to just write off. If he maximized his physical abilities - or even came close - I think you'd be hearing a lot more hype for him in the top-5, despite the rumors.
I agree that the rumors aren't the only thing keeping him from being a top 5 type of player. It's more than rumor at this point. He didn't have good reviews out of Michigan, where things got messy between he and the team. I believe (or rather, I've been told) his first year of starting at Arkansas, Bobby Petrino kind of laid his neck on the block a little by saying he was having a tough time getting Mallett to take bowl preparation seriously. There are rumblings that SOME of his teammates don't really like him, although clearly that does not include D.J. Williams, who is a very high character individual. And, if it's Greg Childs or some of his dumb **** offensive linemen, then I wouldn't be shocked nor concerned because there were times when they were much more of the problem than Mallett...and the only way he probably pissed them off was by calling them out on it as a leader should.
This "sounds like Eminem" stuff is nothing short of hogwash, but it does have to concern a team that he seemingly can't get in front of a camera or in interview without pissing off a multitude of fans and media. There's some thought out there that Cam Newton needs to go to a city where they don't have media with an attack-dog mentality, but I don't buy that at all. I think it's Ryan Mallett that could potentially languish and represent his team poorly in that setting. Newton has been able to brush off attack after attack after attack, with just a smile and a "no comment". Mallett seems to have thinner skin, gets defensive, and from the standpoint of what the PRESS took away from it (whether that's fair or not, and I don't think it is), he absolutely flunked his media appearance at the Combine. So he's going to go to a city where the media aren't going to like him, because for whatever reason they're always put off by his persona, and a number of fans are going to be put off by him as well, talking all kinds of hot, ignorant garbage about "wanting to be Eminem", and so what happens if he struggles early in his career? The media smell blood, they think they can get a Ryan Leaf type reaction out of him if they attack, and so they absolutely will. The fans will be inclined to boo him, because he doesn't have much charisma. This all will increase the stress on Ryan Mallett, and sometimes he doesn't do so hot with stress and pressure.
The drug thing is also PROBABLY true, to the extent that he's probably admitted to teams that at some point in his college career (probably the year he had off and wasn't playing football) he did partake of some. I notice that even in his denials he tends to point to the fact that he never failed a drug test. His message seems to be, I did it when I was off from football but it never interfered with football ever, and a few mistakes do not make me an habitual drug user. If I was an habitual drug user I'd have failed drug tests. When he seemed accusatory about who released the information and when, he was probably talking about whatever primary source stepped forward as a "witness" to him doing drugs. And indeed, the timing and motivation of that person(s) is questionable. Nonetheless, he probably did them and he probably admitted that to the teams, and that's going to legitimately ding his draft stock.
All of this is enhanced by the confidence bordering on arrogance that he displays on the field, and all of it is a concern.
But, I do have to say, I know people who knew Peyton Manning in college and high school, and they thought he was the mightiest of d-ckbags. And I'm pretty sure there are people that would attest to the fact that he's still one. The difference is Peyton knew how to hide it from the media, turn that ****iness into charisma. If Mallett had a little wind in his sails from success on the football field, and I do believe that's a strong possibility because he's a very good football player, then with time he could learn to do the same...to the extent that guys like Peyton Manning, Tom Brady and Ben Roethlisberger have all similarly hidden their @ss from the camera.