Not the ones I’ve seen you can take the dolly out and run just the trailer if not too heavy that another axle will not be required they even have lights on the dolliesMost likely find with this heavy haulage unit the " second" fifth wheel will be a ball bearing turntable , essentially a massive bearing and not a detachable fifth wheel in the normal sense .
Some heavy haulage units the main fifth wheel is this ball bearing type and the neck never leaves the unit in the traditional sense so the outfit is one entity when coupled to the bed.