The 35-year-old hung up his boots at the end of last season after a four-year stint at Zebre and is keen to help develop some of Italy's promising young players.
"It's a real honour to be a part of the coaching staff at an important club like Treviso," he said.
"I have a lot of faith in the people working at the club and I believe that together we can help the team grow in the best way possible.
"I can't wait to start working with the boys who I have played alongside and with some of the most promising young players in Italian rugby."
Goosen, who has worked as both an assistant and head coach, will work on the defence, while former Italy hooker Ongaro joins as forwards coach and Galon as technical coach as Crowley puts his mark on the team ahead of next season.
"The ambition is to contribute to the growth of the team in the areas where we have fallen behind, and to ensure that players have fun playing rugby," Galon said.
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