The veteran center would make be a logical addition for the Mavs with a portion of the mid-level exception as an insurance policy if nothing else. The Mavs' center position is in flux. Brendan Haywood is an unrestricted free agent and Erick Dampier is on the trading block.
The Mavs could ultimately retain both, one or neither. Grabbing O'Neal gives the Mavs a steady presence down low for a cheap price.