Hi Chris,
rebreathers have been used in caves for quite a while, largely because they were available long before open circuit gear designed by Gagnan and Cousteau. Britain's first cave dive was at Wookey Hole in 1935, more than a decade before one could buy an Aqualung. That cave is still dived with rebreathers, John Volanthen and Rick Stanton set a new British depth record there in 2004, more than a mile into the cave and 245 feet deep. They were using sidemounted 'homebuild' rebreathers, squeezing through a tight spot that stopped Rob Palmer almost 20 years ago. And have pushed further since.
In the 80s Rob Palmer used Carmellan CCRs (modified Biomarine units) during his exploration of the Andros Blue Hole in the Bahamas.
The
U.S. Deep Caving Team under Bill Stone used the mighty Cis-Lunar CCRs for their Wakulla explorations.
Since then the
Wakulla Karst Plains Project has been using semi-closed circuit Halcyon/Brownies PVR-BASC and Halcyon RB80 rebreathers. The latter are also used by their Eurpean brethren, the
European Karst Plains Project. Among them are many record setting push dives exploring the deepest and longest cave systems in the world.
For most part either RMV keyed SCR like the Halcyon are used for caving, or electronic CCRs like the Cis-Lunar. Aside from the DIR crowd which uses the Haclyon, various like units are build and popular in Europe. Here in the US you're more likely to find Inspirations, PRISMs, Megalodons or the new O2ptima. Especially the Meg has been embraced by FL cavers due to its strong build quality (the housing is made from heavy duty aluminum). Although most all rebreathers have found their way into one cave or another, from converted Dolphins to retired MK15s. There are several cave CCR instructors, most in FL, but also Mexico and the UK.
The main advantage and reason for their use is the extended range they allow due to their much lower gas consumption. Many of the deep exploration would simply be impossible from a gas supply and logistic standpoint. For bailout, either dual rebreathers, bailout rebreathers and/or OC gas supply are used, depending on the group or individual that does the diving.