Derek Sherinian is confirmed to use the Korg Z1 synthesizer, as detailed in his Leopard Room Gear List featured on Music Gear Review.

Per this May 04, 2021 feature from gearnews.de:

Now a more technological phase begins and there are several interesting mixes with strong use of the TR-909. The nineties are almost at the end and Front by Front has long been recorded. Their sound with the "emulator" as the center was still considered THE appearance. In the phase after that, the emulator disappeared. A Nord Lead is spotted on stage but also a Korg M1 or a Korg Z1

Between the Korg Z1 and the Triton, the sounds are all there for me. I'll occasionally use samplers when working on film and TV music, especially if I need some crazy loops or grooves, but mostly I use my Korg synths.

In an interview with KMAG Black Sun Empire say "We have two rooms. The main one and the small one are almost the same when it comes to PCs and synths; Cubase5 with RME soundcards, Nord Modular G1 and G2 and some random machines like Waldorf Pulse, Korg Z1 and an Evolver Keyboard."

At Glastonbury 2002, Faithless performed using a Korg Z1 synthesizer, as seen in the concert footage on YouTube.

Equipment & Software used on 'SYNTHWAVES':THORSTEN QUAESCHNING: Software: Steinberg Cubase 8 &8.5Hardware: Manikin Schrittmacher Step-Sequencer x 2Manikin MemotronRoland Jupiter 8 synthesizerRoland JD800 synthesizerDave Smith Prophet 8 synthesizerARP Solina MK2 string synthesizerKorg Wavestation Ex synthesizerWaldorf Microwave synthesizerMoog Voyager monophonic synthesizerModular synthesizerRoland V Synth synthesizerKorg Z1 synthesiserKorg Prophecy synthesiserKorg M1 synthesizerClavia Nordwave synthesizerYamaha TG77 synthesizer moduleRoland System 1 synthesizerRoland JU06 synthesizer moduleKorg MS20 monophonic synthesizerRoland JP08 synthesizer moduleRoland TR-8 Rhythm Performer drum machineOberheim DMX drum machineRoland Promars synthesizerFender Starcaster guitarFender Telecaster guitarFender Stratocaster guitarScrewdriver on wood and contact microphones,Several boxes with contact microphonesA field recording of bees in Thorsten's garden, edited on Cubase and then treated with Melodyne & Halion - and finally used for the lead melody line on 'A Calm But Steady Flow'.(Software synthesizers): Spectrasonics Omnisphere synthesizer, Spectrasonics Keyscape

When asked in this reddit thread what kind of equipment Optical uses, he responds:

"I have owned (and still do mostly) as best as I can remember: Mackie 32/8 32 channel - (I have had 3 altogether), 3 x Emu E6400 Ultra (also E6400 orig), Akai S750, S900, S1100, S3000 samplers, Alesis Quadraverb, Focusrite Green Eq x2, Focusrite Green Compressor, Focusrite ISA430 Producer Pack, Lexicon Alex, Lexicon MPX1, Alesis MidiVerb4, TC Electronics Fireworx, TC Electronics Finalizer, Joe Meek VC1, Drawmer MX40, Sherman Filterbank, CryBaby Wah Pedal Boss Pedals - Too many, Novation Basstation, OSCar, Sequential Circuits Pro1, Prophet 5, Wurlitzer, PPG Wave 2.1, Neumann TLM 105*, Fender Strat 1972, Oberheim/Viscount GM1000, Korg Z1, Kawai K1r, Otari Status 16R Mixing Console with Eagle Automation. BSS DPR-402 Compressor. and more I can't recall right ow ;o)."

*The Neumann links to the 103 because the moderator who approved this post believes Optical wrote 105 by mistake. If anyone believes this to be an error please follow up in the comments section so that we can adjust :)

In a Tech Talk segment on Electronic Beats TV, Ian Pooley discusses his Berlin studio setup, including his use of the Korg Z1 synthesizer.

in this video we can see s.p.y using korg z1...

Not that Isham has entirely forsaken his 'synthetic' past — far from it, in fact. Even his beloved analogue collection — now expanded to incorporate an Oberheim Xpander, a Roland MKS80 with MPG80 programmer, and a rare Moog Model 12, one of those 'big modular Moogs' he once admired from afar — regularly gets a look in: "I just did an entire film score that used the 2600, MIDI'd via an old Roland MPU101 MIDI‑CV converter" says Isham, with a hint of bravado. Isham's studio also contains an extensive selection of more modern synths. Of his Korg Trinity Plus, Z1, Prophecy, Wavestation A/D and ubiquitous M1, Roland JD800, and newly acquired, knob‑laden Access Virus, the latter is currently proving most agreeable with the composer.

Talking about his outboard gear, Bola mentions:

"I’ve also got a Korg Z1, which I’ve had for years. I won’t get rid of it because it’s quite unique and typically Korg. It’s fantastic for pads and textures and you get lots of control.”

Clive uses a Z1 in this Pendragon video.