There is only one slight problem, in that freediving is focused on taking a full deep breath of air and holding it, whereas with scuba, Cousteau's Rule #1 is "Never hold your breath... ."
The historic NAUI and YMCA way of teaching scuba was first to teach you freediving together with many freediving skills, then to subsequently wean you onto the scuba gear. This is also how scuba diving skills were first developed, by Florida and SoCalif (and French and British and Italian) freedivers. That is also how I learned. We became freedivers first, then scuba divers second. This is also how I taught my wife, since I wanted her to learn the traditional approach as well, and I wanted her to get used to the ocean with fins, mask, and snorkel before being incumbered with tanks and gear.
There is a drawback to this approach, in that it tends to reinforce the breathholding practice, even during the scuba phase. The habit is unconscious. You do not realize you are doing it.
I do not teach scuba students to be freedivers first. I teach them "Never hold your breath on scuba." The reason is risk related and insurance related. And therefore that also rules out freediving training before scuba, in my opinion.
With my wife, I had the luxury of being able to take all the time in the world to teach her, first snorkeling, then freediving, then scuba, then nitrox. You do not have that luxury with a class of students.
Having stipulated those paradoxes, there are mask clearing skills you can do just fine for snorkeling. Go over in the shallow end of the pool, sit on the steps, make sure you can breathe through your snorkel while sitting underwater, with your snorkel sticking out of the water, then flood your mask, and clear it, while you continue to breathe on your snorkel. That will help you with mask clearing on scuba as well.
There are also fin skills that you can practice while snorkeling, such as snorkeling on the surface, then trying to fin backwards with your fins only. This works as well on the surface with snorkeling as it does underwater on scuba.
Strengthening your frog kick fin technique can also be practiced while snorkeling on the surface. A small frog kick is the most efficient way of propelling yourself underwater, rather than a big flutter kick. Most instructors do not teach this in basic open water, and so you must wait to learn it yourself from the divemasters at the exotic warm water resorts (Florida Keys, Hawaii, Mexico, Caribbean, etc.)
Blast clearing your snorkel is a good way of developing comfort with blast clearing your scuba regulator as well. You can practice that anytime your snorkel gets water in it.
I do not believe it is necessary or wise to teach everyone to be freedivers before scuba, simply because of the short time that is now involved in most basic open water courses. And there is not time to learn and then un-learn breathholding.
Snorkeling on the other hand has some good applications before scuba, which enhance scuba skills later.
