Olshey's second season he acquired Mo Williams who was an allstar. The next offseason he acquired Chris Kaman. Of course he also added Melo. The Blazers haven't acquired an allstar in the Cronin era so yes DeRozen would be his first. Back in 2006 Steve Patterson was able to acquire Jamaal Magloire.
Now if your talking about the Blazers acquiring a player who was an allstar the prior season; I'm not sure they have ever done that in franchise history? Even Scottie Pippen and Steve Smith were not allstars the year prior to coming to Portland. So maybe Cronin can really try to sell acquiring DeRozen as a historic GM achievement.