It would seem to make intuitive sense that good cardiovascular fitness would lead to better air consumption. It is however a difficult one to prove as there are so many variables at play. I can’t find any strong studies on this subject and think that it would be fascinating to conduct one.
On one hand you have fitter people being able to make better use of air relating to exercise but on another you have increased muscle ratio and higher metabolism burning more calories at rest.
Yoga has certainly shown many benefits in diving; it helps stress management, improves mental alertness, teaches you how to relax, improved use of senses, increases flexibility and concentration on breathing techniques.
Overall it would seem to make sense that as in any sport, a diver should maintain some degree of physical fitness.