NBA Summer League July 10th-20th:

[SleepingHero]

Can we read anything into OMax's absence from the SL roster? I don't know if he's ineligible, but it would be a chance to show him off to potential trade partners.

The rules on NBA summer league rosters are pretty open. Anyone is eligible to play. The only restrictions teams have are as follows:

No NBA Team may simultaneously enroll more than four (4) Veterans in any summer basketball league during an off-season. For purposes of this Section 4(a), the following players are not considered Veterans:

• a player who has never signed a Player Contract or whose
  first Player Contract begins with the Season immediately
  following the off-season in which such summer league is to
  be conducted;
  
• a player not under contract to an NBA Team at the time he
  enrolls in such summer league;
  
• a player under contract to an NBA Team but who missed
  twenty-five (25) or more of the Team’s games during the
  Regular Season immediately preceding such off-season due
  to injury or illness; and
  
• a player who played for a team in the NBAGL or any other
  U.S.-based professional league during all, or any portion, of
  the Regular Season immediately preceding such off-season.
  

OMax would be considered a "vet" but looking at the Mavs summer league roster it doesn't appear like they are limited by this rule. Typically players who have "graduated" summer league never return. Maybe the Mavs feel like  OMax has graduated and won't really gain any benefit from playing against rookies. Maybe they don't value OMax anymore. 

Point is, not much can really be read into it. Hardy isn't on the roster and neither is Brandon Williams.