"He's all-in and ready to go," Gruden said. "That's my understanding. Really happy to have him out here. He's a great player."
Earlier, during the media viewing window, Brown took part in a pre-practice walk-through before retreating to the weight room, changing into cleats from sneakers and then returning for the end of the team stretch period. At that point, he never had a helmet in his possession.
Gruden told reporters that there's been "no distractions" for him or the team concerning Brown, whose second grievance hearing with the NFL will be presided by the same arbitrator from his first hearing and is scheduled for Friday morning, a source told ESPN's Josina Anderson.
Brown's grievance is the latest part of Brown's ongoing fight against an NFL policy that requires helmet certification according to industry standards.
"If you see a distracted football team, then I disagree with you," Gruden said. "So, I'm not going to make any more of it than that. There's a lot of teams that are missing star players.
"It's not been a distraction to me, at all. ... This grievance thing is no laughing matter; it's something that's really important to him. And there's nothing wrong with supporting your players, on things that they believe in. We also understand the league's position, but I'm confident that he's going to be a heck of a player for us and be ready to roll."
Brown's agent, Drew Rosenhaus, told ESPN Radio's Golic & Wingo on Wednesday that his client will play this season, even if this second grievance is denied.
"There's never been the possibility that Antonio would let this prevent him from doing what he loves to do and fulfilling his destiny as one of the great receivers of all time," he said. "He is determined to play this year and what we're trying to do is get him in the safest equipment possible."
Brown left the team twice in training camp in Napa, California -- the first time for two weeks to ostensibly seek treatment for his frostbitten feet; the second time on Sunday, skipping out on practice in anger over the league denying his helmet.
It prompted an "all-in or all-out" ultimatum from general manager Mike Mayock on Sunday.
The team broke camp in Napa on Monday and began working at the team facility Tuesday.
The Raiders play the Green Bay Packers in their exhibition finale on Thursday night in Winnipeg, Manitoba.
Gruden earlier said he anticipated taking everyone on the road, but he was doubtful that starters would play.
Brown, meanwhile, addressed the microscope he's been under in a teaser for the next episode of HBO's "Hard Knocks" on Tuesday night.
"The feet feeling a lot better," Brown said in the clip. "I got brand-new skin. Got it all trimmed up. It's been a journey, man, but I feel a lot better. Working with the NFL, getting the right equipment, I've been working hard on the side. I've been going, taking care of the feet. So, I mean, I want to give it to my teammates, so, hopefully, soon get out there and get to work.
"You know, too much noise right now. More work, less noise. I feel like I was enemy of the f---ing state. F---. Getting the feet trimmed up. I'm on every channel. Because AB is actually a good player. A really good player. And he's a handsome-looking player, by the way. So that's all it is right there."