In the commercial realm versus a homeowner DIY effort,
we would have to be first looking at the label of the product. Is it labeled as
a fumigant or deterrent for snake use?
If not then commercial off label use would be prohibited by law.
I'm sure we have all witnessed a myriad of chemical concoctions utilized
for species they aren't approved for and therefore violate state and federal laws
(Not that folks are getting caught or reported often).
I've been in attics where there are over a dozen cans of fumigant that have been deployed
to rid the homeowner of some form of mammal none of which are on the label.
Ultimately could a fumigant drive out snakes? Yes.
Is that fumigant in this country being used illegally? Most definitely.
As you say though, what is your measure of success when you can't see the results?
We all know what is legal and what is practiced are two very different things.
We who do follow the laws and regulations set by governing bodies do well to stay on
that side of things and to assure we know the laws and pass that on to homeowners
when we hear erroneous information being disseminated.
The only fumigant for snakes I've ever heard of is utilized to keep brown tree snakes from
getting on aircraft and off of places like Guam where they can spread to other global locations
causing negative impacts to bird and mammal populations.
Just my .02
Justin