Although I think the NBA has some problems, I would not even begin to believe anything that Donaghy says. He has zero credibility. So, no matter if there is truth in what he says or not, you have to consider the source.
Source considered, I believe that, like in jokes, even stories like this have at least some truth in them.
It doesn't help that there's footage of those games and they're clearly rigged, or just very, very badly officiated...
.edit: and that's 3 out of 6 posts in this topic with my ridiculous face on the side. I'm going to hold silent for a bit now while the topic evolves 
Also, not sure if anyone remembers, but I think Ralph Nader at the time was suggesting an inquiry into Kings-Lakers Game 6 because of the appearance that the refs were clearly trying to get the Lakers to tie the series. When a politician is demanding an inquiry, there is probably some reality to the accusations.
It also doesn't help when David Stern was so quick to try to sweep this under the rug, with the "It was a rogue official so let's all move on. Seriously, let's move on right now!" stance on the matter. By most accounts, Donaghy is a jerk and a terrible person, but that doesn't automatically make him a liar about everything.