So I listened to the clip and read as much as I could on Joey DeMaio.
He's using full-scale 8-string in the clip. He's also known to use 4-string picolo/higher pitched strings at full-scale also. His main bass is a Rickenbacker 4001 that had the neck sanded down narrow using light strings, and all hardware/pickups replaced, bridge/nut especially to get the string to string distance narrower. (According to his tech, he's broken the neck 3 times so far.)
Looking around for 8-strings and short scale is a small set of options. I only found a Hagstrom, Warwick and Spector (30"-32"). Warwick looked like the best quality to me, Spector the second maybe (could be wrong - I haven't played them). All were around $1000 USD. The Washburn/whatever custom he's using in the clip is full-scale, though.
For short scale 4-string basses using picolo tuning, there's a few ways to go that have more options than the 8-string idea.
- Short scale bass with lighter strings tuned up. When I bought my short scale bass, I tried Gibson, Squire, Ibanez and Gretsch and I ended up buying the Gretsch. Was very solid, heavy, good solid sound, like a full thumpy Fender Jazz bass. You could get one of those, put lighter guage strings, tune up, and adjust the truss accordingly. For lighter strings, you could take the top strings out of a 6-8 string bass set, or take the low strings off a baritone guitar set.
- Baritone guitar with only 4 strings on it. There's photos of DeMaio actually having done this on some occasions.
- 8 string guitar, just use the low 4
- 8-string bass with only the high strings on it. (However, the string to string distance is much wider than DeMaio plays.)
- Find a used B.C. Rich 10-string and just use the middle 8 strings
Also, he splits his signal, so there's a mid-treble portion that is distorted like a guitar and a bass portion of the sound that is totaly clean. John Entwistle of The Who used to do the same trick. So you'd need a bass amp and a guitar amp; or two bass amps EQ'd differently and the brighter one with a crunch pedal in front of it.