To make room on the 40-man roster for the additions, the D-backs outrighted left-hander Miguel Aguilar and right-handers Kevin Ginkel and Riley Smith to Triple-A Reno.
Following his addition to the 40-man roster, Robinson was placed on the restricted list while he continues to work through legal issues stemming from a 2020 arrest.
By putting Robinson on the restricted list, the D-backs' 40-man roster stands at 39, meaning they could select a player in the Rule 5 Draft if they choose. When Robinson is again eligible to play, the D-backs will have to clear a spot on the roster for him.
Robinson cannot be selected by another team in the Rule 5 Draft.
The highly touted outfielder -- ranked as the club's No. 8 prospect by MLB Pipeline -- has completed the community service that was required for the charges against him to be reduced to a misdemeanor.
"I don't have all the exact specifics on what the legal ramifications of all this could be," general manager Mike Hazen said. "But I know the first step that we were trying to accomplish was for him to get his community service done as directed. I am very happy that he went out and did his community service, with the urgency that he went out and did his community service with. And from all indications that I got from everybody was that he did extremely well and he was very diligent, as he should have been. So that part, I am happy that he went, and we're hoping for the best moving forward."
Hummel was acquired by the D-backs from the Brewers in exchange for third baseman Eduardo Escobar at last year's Trade Deadline. In 198 plate appearances for Reno after the trade, Hummel hit .353/.429/.575 and earned a trip to the Arizona Fall League.
"Cooper we acquired in the middle of season, and he performed the way we expected all the way through the Fall League," Hazen said.
Weiss, the D-backs' No. 30 prospect, split time between Reno and Double-A Amarillo, averaging a combined 10.1 strikeouts/nine innings while both starting and relieving.
"We just think the stuff took a major step forward this year," Hazen said. "Pitching at both ends of our upper levels in extreme [hitter-friendly] environments while doing a good job. We just felt like the way he performed and the stuff he has, that we want to give him a chance coming in to Spring Training and didn't want to expose him [to the Rule 5 Draft]."
A few notable names the D-backs did not protect include infielder Buddy Kennedy and right-handers Levi Kelly and Matt Tabor.
Players first signed at age 18 or younger must be added to 40-man rosters within five seasons or they become eligible to be drafted by other organizations through the Rule 5 process.
Players signed at 19 years or older have to be protected within four seasons.
Clubs pay $100,000 to select a player in the Major League phase of the Rule 5 Draft. If that player doesn't stay on the MLB roster for the full season, he must be offered back to his former team for $50,000.
For this year, that means an international or high school Draft pick signed in 2017 -- assuming he was 18 or younger as of June 5 of that year -- had to be protected. A college player taken in the 2018 Draft was in the same position.