I'm not sure whether the trait of strength or the trait of character is associated with being a dope; I clearly have respect for Manuel as a person.
The Bills are going to sign a veteran to carry for the rest of the season. Whoever that guy is, he is going to be the only veteran QB on the roster. He is going to be in EJ's ear when they practice, when they're in the film room, during games, at meetings, in the morning, in the afternoon and in the evening. As the only veteran at his position on the team, he is going to serve as a role model for Manuel by default.
If it turns out that Freeman spends too much time in the clubs, or is a locker room lawyer, or spends too little time in the film room, or likes to submarine his coaches, or whatever, that IS going to have an influence on how Manuel views the role of an NFL QB.
Since I consider the upside of adding Freeman to this roster to be minimal at best, then even any minimal downside makes the acquisition questionable.
The Bills aren't going anywhere this year; if they have reliable reports that Freeman is a bonehead at all, then bringing him in here accomplishes nothing and is potentially a net negative.