Most of those devices use standard AA/AAA type batteries that don't blow up if misused. The big question is if any HIGH POWERED flashlights that use 18650 batteries, for example, are UL certified. I stress high power because in order to be a good acid test of potential certification the flashlight would need to be capable of discharging at the same rates we discharge our mods. Or a reasonable rate (say 50W per 18650 battery).
While you may be correct, UL has not specifically said they require fixed only packs in ecigs, they didn't say they didn't require them either. Remember the UL is NOT there to protect consumers from themselves, if I plug a PB&J into a VCR and burn my house down, that's on me. They are there to make sure a product is properly manufactured and can stand up to basic scrutiny and tests. In other words mods that claim to be able to do 300 watts with 2 18650 batteries will never pass. Mods that claim to have short circuit protection but it fails, will not pass. Mods that do multi-battery charging but do it unevenly or don't have overcharge protections will not pass.