Yes, they are. I wish Brian limited it to one acronym, but there are two. Free Swinging or High Energy Tweeter. Free-swinging means the diaphragm is supported only on the 2 ends, a quality necessary to be labled a true ribbon vs. a leaf tweeter or quasi-ribbon.
The dual acronyms are not as bad as the "Dipole Surround", which has a bipolar radiation (the $1200pr MSRP Dipole Surround SEs, updated about a month ago, are superb matches for the ribbons with virtually identical voicing). Highly recommended as side &/or rear surrounds with the ribbons up front.