In a tweet, Del Rio wrote: "Never liked league rules that eliminate the ability of teams to offer Aldon and others in his situation the structure they so desperately need."
Del Rio coached the Raiders for three seasons before being fired after the 2017 season. Smith played nine games under Del Rio in 2015 before being suspended Nov. 17, 2015, and has yet to be reinstated.
Del Rio did not elaborate on his initial tweet, but league rules bar suspended players from practices and team meetings. Del Rio's comments reiterated his stance from last March.
"It's a little bit frustrating to not be able to be a part of the process," said Del Rio during last spring's owners meetings. "My feel is that I could help him, but the experts know. The experts don't allow that. We have to follow the rules.
"It does get frustrating to not be able to help a young man and provide support and provide structure. Somebody else has to make those decisions."
The Raiders released Smith after he checked into rehab after an alleged domestic violence incident, which was reported by TMZ.
San Francisco police were searching for Smith after he fled the scene Saturday night.
Shawna McKnight, Smith's fiancée, suffered injuries that were not life threatening. She told TMZ that her family brought Smith to rehab. Smith proposed to McKnight on Valentine's Day.
Smith has multiple DUI arrests and a weapons charge on his record. He also was investigated for domestic violence in February 2017.
Smith, 28, the seventh overall pick in the 2011 draft by San Francisco, was named first-team All-Pro in 2012. He recorded 44 sacks in 50 games with the 49ers before registering 3.5 sacks in nine contests (seven starts) with Oakland in 2015.