when they signed him, they ran a 4-3
and yet in that 4-3 scheme, he was not expected to be primarily a pass rusher. which is what he is.
I remember Haynesworth nagging about it during the season, how the DC's scheme involved him rarely being able to go after the QB.
Scheme is not all about the formation, but also the player's role in the formation. Haynesworth is a pass rusher who is being paid not to rush the passer.