AFAIK, the grit's from his cranked tube amp (an SVT-CL at the time, I believe), and there's no chorus (there MIGHT be a little post-recording reverb added, though, or it might just be natural room ambience).
Bello has a great heavy pickstyle tone, though. I especially love the cover of "Got the Time".
Bello has generally been a bass-to-amp player, but TBH, I haven't had a chance to listen to his work in Helmet... so I'm not sure how that may have changed. All my exposure to his work is through Anthrax (which I'm a big fan of).