EC, don't be ridiculous.
It's marketing. Forget about the salary cap and contrast $80k on Rodman against $80k of back of bus ads (waste of money), radio ads (probably not much better), etc. They could get him over and get on the news for free 3-4 times over the course of the event (lead-up, day of game, day after, etc). If they sell a few thousand extra tickets on the day and then pick up a few more season ticket sales over the course of the year, they could well pay off their expense.
Pretty much everyone is spending over the salary cap.
If Dusty Rychart retired, but made a cameo appearance for North in a pre-season game one day, and you went along to watch, would you be an idiot?
There are a tonne of people who followed the NBA during its peak in Australia but no longer go to NBL games who would go to this event - I think you'd even get a few people coming in from interstate for it.
One OzHo coaching in Melbourne said he got to training and all his kids were immediately asking if it were true that Rodman was going to play for the Dragons - these are all kids who don't go to NBL games.