Yes, it's true. At the end of 2004, DG announced that Shuji Kondo, Shogo Takagi, brother YASSHI, Takuya Sugawara, and Touru Owashi were all fired. At the 1/9 show, Okamura said in a statement that all members of the DG roster were to act accordingly, both inside the ring and out, giving CIMA and Magnum TOKYO as examples of other stars who would be booted if they acted improperly.
The five fired wrestlers apparently found out they were getting their walking papers from the Florida brothers. After they were fired, the five guys basically all indicated that they were going in different directions, and that they would never ever fight in a DG ring.
As for why exactly this happened, it's hard to say. From the behavior of the five guys after their firing, it seems that they're just resigned to their fate -- a sure sign of being guilty of something. Who knows?
"I think the basic thing nobody asks is why do people takes drugs of any sort?... Why do we have to have these accessories to normal living to live? I mean, is there something wrong with society that's making us so pressurized, that we cannot live without guarding ourselves against it?" - John Lennon