I never found a reason or had a requirement to use ACF Google Maps custom field, when Formidable's Geocoder add-on captures everything as it is. You may need to update the ACF field in the frm_after_create_entry and frm_after_update_entry hooks.

Yes, you are correct. My solution in the end was to use Formidable's geolocation as the coordinates interpreter, and store the resulting lat/long and input location into standard ACF Text fields. I can then use the lat/long to power other things for display on the front end. Specifically, I'll be doing a mapped, filterable database with FacetWP and I only need lat/long for that.
I had to do some digging in the Formidable docs, to figure out this method, since the technique is kind of buried deep in there. The docs could use some improvement, both on both the ACF page and the Geolocation page.