Tomsula is particularly impressed with Hayne's ability to catch high balls, a sign the club may have him pencilled in as a punt returner.
Hayne, the former Parramatta, NSW and Australian rugby league backline star, has had little trouble transitioning to catching gridiron balls.
"Did you see him catching those punts?" Tomsula told reporters on the eve of the 49ers' rookie mini-camp.
"It's a little easier to catch a football than it is a rugby ball.
"The wind gets that rugby ball, that thing's zig-zagging all over the place."
Hayne shocked NRL fans last year when he announced he was quitting the sport to take a chance at an NFL career.
Hayne turned his back on a lucrative contract with Parramatta for an offer from the 49ers that guaranteed just $US100,000 ($A123,000).
Tomsula is impressed by Hayne's dedication to making it in the NFL, describing Hayne as "the man in Australia".
"He gives that up and he comes here to do this, and he starts at the bottom of the totem pole," the coach said.
"That says a lot to me.
"Again, he's still, when you watch what we're doing here, he's still playing rugby.
"There are no pads here. He's fielding balls and running around in shorts and a T-shirt.
"Am I thrilled that he's here? Absolutely.
"He's a neat dude."
The 49ers will cut its current 90-strong team to 53 players on the eve of the 2015/16 season in late August, although Hayne could also make it on to a nine-man practice squad.
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