Neemon and Bokomon are actually Ghostbuster allies Louis Tully (the company accountant) and Slimer (the babbling, gluttonous mascot). Why they've been turned into two useless Digimon is an even bigger mystery than the transformation of the Ghostbusters into the DigiDestined--until the very end, when Ophanimon's plan is revealed.
Veemon looks like one of the Digimon on TV, but he doesn't act the same, and Digivolves to a different Champion level form, Veedramon. He's been sent to help the Digibusters by Ophanimon, the Celestial of Light. He later gets to use the Golden Digimental of Miracles to become Magnamon
Seraphimon is the Celestial of Hope, and one of the rulers of the Digital World. His data was absorbed by KingEtemon; it de-digivolved him to his Rookie form of Patamon, who interestingly enough has the exact same voice as Janine.
Ophanimon is the Celestial of Light, and the other ruler of the Digital World. She's hidden her power to prevent KingEtemon from getting it, and regressed to her Champion form, Gatomon.
Leomon is a wise and noble warrior. He's also the Kenny McCormick of Digimon, and in keeping with that tradition, he's killed by KingEtemon while covering the Digibusters' escape
Hanumon and Thunderballmon are a couple of squabbling morons who mostly defeat their enemies with dumb luck and a brain-deadening assault of stupid tangents and non-sequitors. Palmon, their travelling companion, is constantly exasperated by their silly antics.
Falcomon has an Austrian accent and is a big fan of Eighties New Wave music. He discovered the ability to Digivolve to Diatrymon while helping Egon, Janine, and Patamon.
Tentomon is the guardian of a forest covetted by TyrantKabuterimon, and fights the oppression with the help of the Beast Spirit of Thunder, which digivolves him into MetalKabuterimon.