3 Primary Ways
1. If the team you are trading to (the Nets) are under the salary cap, the Nets are not required to send back equal salary. They can absorb that contract if they have room under the salary cap. So if they are 50m below the salary cap, they can easily absorb Jrue's contract without being required to send back equal salary.
As an aside, when this happens, it creates a trade exception equal to the salary absorbed. So in the above example, the Celtics would receive a trade exception equal to Jrue's contract size next year.
That leads to the second primary way...
2. Players can be absorbed into those trade exceptions. Most teams have at least a few small trade exceptions, but a few have pretty big ones as well. If a team has a trade exception big enough, they can completely absorb a player's contract without needing to send back equal salaries.
Unfortunately, I don't believe there are any big enough out there for Zinger, White or Holliday's contracts. There are some big enough for Hauser's contract though.
3. The third and least effective way is that, depending on the team, they may not need to send back the full amount of salary to match. A 2nd apron team like the Celtics do, but 1st apron teams and non-tax teams can receive up to 125% of the salaries they are sending out. That's what would allow us to trade for Vassell at 26m for Jrue's contract at 32m. That would allow us to cut about 6m. Again, not a lot, but could certainly help.