Rod Giddens wrote in an email to The Associated Press that Dareus was allowed to enter the program during a hearing at Calhoun County Court in Alabama earlier in the day. Dareus attended the hearing while being excused from training camp in suburban Rochester, New York.
Buffalo's WKBW-TV first reported the agreement.
Dareus, who is from Alabama and played for the Crimson Tide, was arrested and charged with possession of a controlled substance and drug paraphernalia after being stopped by a state trooper on May 5.
The charges will be dismissed and potentially expunged should the 2011 first-round draft pick successfully complete the program.
Giddens referred to Dareus as "a humble, gentle giant of a young man, who needs some mentors."
This marks the first positive step during what's been a troubled offseason for Dareus.
Four weeks after being arrested in Alabama, Dareus was allegedly racing teammate Jerry Hughes when he crashed his 2012 Jaguar into a tree near a busy intersection not far from Ralph Wilson Stadium.
Dareus was charged with reckless endangerment and ticketed for several traffic violations, including drag racing.
Dareus is still attempting to resolve those charges after failing to accept a plea deal earlier this month. He is next scheduled to appear in court on Sept. 9.
The NFL could potentially discipline Dareus with a fine or suspension.
Dareus also faces an immediate on-field challenge.
After reporting to camp on Friday, Dareus was placed on the active/non-football injury list after failing a conditioning test on Saturday. Dareus must pass the test before he can be cleared for practice.
Coach Doug Marrone said Dareus was scheduled to return to camp on Monday night, and was expected to be working out on the sideline during practice Tuesday morning.
Marrone didn't provide a timetable of how long it might take Dareus to be tested again, except to say "when our weight coaches feel that he's ready."
Dareus has already missed the first two days of practice.
At practice on Monday, starting linebacker Brandon Spikes was escorted by trainers to the team's cooling-off tent after experiencing what Marrone described as cramps. Marrone didn't provide an update on Spikes' status.
The 2-1/2 hour practice was held on a muggy afternoon with temperatures in the high 80s. As a precaution, Marrone took a 10-minute break during practice to allow players to cool off and hydrate.
The Bills avoided a scare when rookie first-round pick receiver Sammy Watkins was poked in the eye. He had to be helped off the field after making a leaping catch between three defenders. Watkins was treated on the sideline and returned for the next team drill.
Earlier in the day, the Bills shuffled their roster by signing defensive tackle Landon Cohen and receiver Naaman Roosevelt.
To make room, Buffalo released receiver Ramses Barden and linebacker Nathan Williams.
Cohen has five years of NFL experience, dividing last season between Dallas and Chicago. He was drafted by Detroit in the seventh round in 2008. Cohen reunites with former Lions coach Jim Schwartz, who is in his first season as Buffalo's defensive coordinator.
Roosevelt rejoins the Bills after spending the 2010 and 2011 seasons in Buffalo. He's a University at Buffalo product and split the past two seasons on the Lions and Cleveland Browns practice squads.