Full time manual focus

Are all L lenses, and all true USM lenses, capable of full time manual focus?

All of the lenses with ring USM have FTM. Also the Canon EF 50mm f/1.4 USM has FTM even though it has micromotor USM. The other USM lenses that have micromotor USM don't have FTM.

Although the currently sold L lenses have ring USM and therefore FTM, not all past L lenses have USM motors. For example the following L lenses do not have USM or FTM:
EF 20-35mm f/2.8 L
EF 50-200mm f/3.5-4.5 L
EF 80-200mm f/2.8 L
EF 100-300mm f/5.6 L

Also the new stepper motor (STM) lenses have FTM such as the EF 40mm f/2.8 STM and the EF 18-135mm f/3.5-5.6 STM.

Yeah, they can manual focus, but they sure are not meant to manual focus. Try a Zeiss lens with it's long throw and you'll never again manual focus a Canon lens.