I think there are at least 2 different kinds of voleos, one that is a embellishment (the type b above), the other is a play with the geometry (the type a above). (i am consciously avoiding talking about "lead" vs. "un-lead" here - the embellishment is lead, too, but the shape is create purely by the followers work, and not by collaboration between the partners). Most boleos (fall somewhere in on that spectrum - even the most forceful leader can not create a boleo if the follower is not letting it happen, and even the most relaxed follower will add some direction and control to an impulse based boleo).
As Mladenac points out an embellishment type boleo will not work if the follower does not "know how to do it", but similarly a lot of followers that have not experienced a geometry based boleo will tense up and stop one from happening (and be wrenched uncomfortably) - so leading it that way is not a guaranteed to work with a follower you don't know either.
My approach to moves is very much inspired by one of my therapy profs - his mantra was "all behavior is functional". I similarly believe that all cool tango moves are there to show off ones skills - the question is figuring out what skill we want to use for something
so i would say: both a) and b) are "correct".
a) is a geometry based boleo (if i understand the description - similarly to UKD i would probably not pivot myself if i lead this, i would use dissociation+embrace to pivot the follower which makes it easier to reverse (forward boleos are a bit tricky because of the way the knee works - in some ways they are actually more like backward boleos after getting the free leg on the outside of the standing leg than anything else, which makes the timing and geometry a bit trickier). The leader needs to provide the impulse and the "whip" (by pivoting/using the embrace/stepping), while at the same time maintaining the followers balance on the standing leg. The follower needs to be aware of which of the legs is the standing leg, and which one is the free leg, and be sensitive to being off axis without being off "enough" off-axis to make it neccesary to step/turn the free leg into the standing.
b) is a embellishment type boleo. The leader needs to convey that they are not going to move more after the sidestep, and suggest that there will be space for an embellishment (what works for is me is suggesting a circular movement during the sidestep by stepping in an arc - basically something that suggest that this is not a cross by softening up the alignment), and they need to give the follower time to do the embellishment at the end of the arc. The follower needs to recognize that there is space for an embellishment there, and trust that the leader will give her time to do it.