Who writes the recommendation letters for returning student PhD applicants after a big hiatus?
I am not aware of a specific rule requiring academic references. It may be more a matter of common sense. If an applicant has recently completed a lower degree, the committee may expect to hear from professors who saw the applicant's work.

I was admitted to a PhD program over 25 years after my master's degree was awarded. What I had done in the last quarter of a century was far more relevant than my last academic experience.

I got references from my manager, my prior manager, and a chief technology officer. The last person was less familiar with the details of my work, but had a PhD and connections to the department where I was applying.