Respectively and invertedly, yes
those are (nylon-core) rounds, and no he doesn't:
MicroBass LaBella Flat Wound Strings | Gold Tone Folk Instruments
^ These are the flats (they also describe them as "tape wound metal", a somewhat old-fashioned way to refer to the outer metal ribbon winding of ordinary, regular flats, not nylon tapes).
Please note GT discourages you from using them on fretted hollow-body MicroBasses, but states that they're fine on solid-bodies and fretless HBs. I'd call for clarification on that warning.
I suspect it has something to do with the fact that the strings are steel-core, thus way stiffer than polymer strings, and would require some moderately aggressive surgery to the instrument in order to move back the bridge for proper compensation (@kohanmike's instruments wearing these have "electric" bridges with individually adjustable saddles). However, on the fretted solid-body model the bridge is also non-adjustable, so...what gives?
A possible, alternative explanation would point to added tension, which might lead to bridge-lift on acoustic models, but they say fretless hollows are fine, so again I got nothing.