Listed on Steve's official Roland page.

"What happened was, for 12 years I always used a keyboard player and a drum programmer for my Roland R-8 MKII, which is a bitchin’ drum machine! The keyboard player and I had a falling out and I wound up sitting in my studio all alone. I was writing songs like “Stronghold” and “Attack” — good riffs if I may say so. But I felt there was something missing, so I went to the store and what did I do? I bought a guitar synth because I just wanted to hear what it would sound like if a keyboard player like Derek Sherinian or someone who could play some interesting stuff on there. Reason being, I didn’t have somebody with me. I just wanted to add something that would help me come up with vocals and lyrics. I write all that stuff. I write every thing, you know? So that is how I use the GR-33."

At 22:48 of this "Rig Rundown" with Premier Guitar we're shown Steve's GR-33.

Chris Broderick mentions on his website that he owns a Roland GR-33 Guitar Synthesizer, describing it as an "awesome musical tool."

Haruomi Hosono used the Roland GR-33 Guitar Synthesizer as part of Yellow Magic Orchestra's setup during their 1980 world tour, as shown in a user-uploaded photo on Geocities.

In this article from BOSS Users Group magazine (Vol. 5, No. 1 Summer 2001), David details his guitar rig at the time, which included an GR-33.

“I have a lot of systems onstage: an acoustic banjo, an electric, a synth system for an electric, a guitar, a wireless system, preamps, and EQs,” he explains. “It's a lot of stuff, so I just use the onboard sounds. Live, the Roland GR-33 works just fine.”

Guitar gear for the album Octopus: Peavey Heritage amp Roland Bolt 60 amp Vox AC30 amp Roland: GR-707 (x2); GR-303; GM-70; GR-33B; GR-300; GR-700 (x3)

As the de-facto lead guitarist, er mando-man, Kang bounces between his Ron Oates Custom 5-string Octave Mandolin or Walker Electric 5-string Octave Mandolin. To amplify his custom 5-strings, he cranks up a Two-Rock Custom Reverb and Groove Tubes D75 Power Amp through a Bogner 2x12 cab. His two-board setup boasts a DigiTech XP100 Whammy Wah, a Electro-Harmonix Micro Metal Muff, a Electro-Harmonix Micro POG, a Electro-Harmonix Micro Synth, a Electro-Harmonix Q-Tron, a Line 6 DL4, a Keeley Phaser, a Fulltone Full-Drive 2, a Keeley-modded Ibanez TS808 Tube Screamer, a Keeley Katana Clean Boost, a Boss TU-2 Chromatic Tuner, a Maxon Compressor, a Ernie Ball Volume Pedal, a Roland GR-33 Guitar Synth, a TC Electronic G-Force, a Sarno Music Solutions Steel Guitar Black Box, and the boxes are powered by a Voodoo Lab Ground Control and a Voodoo Lab Pedal Power 2+. And his uses various Elixir strings and Fender Extra Heavy picks.