If you click onto Bolt21's SLERS guide down at the bottom they do say ATF is a user on the state system
Just to clarify, they are an "interoperability" partner, not a full blown SLERS partner. My county's sheriff's office is an interop partner, but they operate on their own in-the-clear EDACS system. However, if the Tampa ATFE were to become silent, wouldn't be a big mystery where they went.
Regardless, seeing ANY agency on the SLERS list makes my skin crawl, whether all-out partner or not.