not saying he'll make the team, but there are likely going to be roster spots available to some of these guys at minimum salary (non-guaranteed) slots
Currently, we have Pierce, Garnett, Perkins, Rondo, Wallace, Davis, Bradley, and Erden. Until Erden is officially waived or Wallace retires, that's 8 sports.
From free agency, we will be looking to sign Ray Allen, Tony Allen and Nate Robinson, a backup wing and a backup big man. That's 5 more slots for a total of 13.
So it basically boils down to some of those summer league players proving they can be more useful than Marquis Daniels, Scal or Shelden Williams as roster filler. That's not a given.
In reality, the roster spots are not as many as it seems -- 2, maybe 3 if Erden is waived. So it might realistically boil down to having to pick whether to waive Erden to pick Parkhauski.