According to the Vortex Springs website, the only restriction is beyond the locked gate. It appears they are inviting experienced divers to explore a cavern:
SCUBA Divers Heaven
For the more experienced divers, the natural cavern is the real deal. 58+ feet deep, it continues through a garage-sized tunnel into cave diving. Meandering gracefully another hundred yards or so to a depth of 115 feet, it has a penetration depth of 310. The tunnel is blocked by a steel grate at this point. The white sand bottom is gently rippled by the outflow from the underground spring. Pockets of air randomly collect at the ceiling, creating a sound like unto gentle piano tones. Guided by a permanent safety hand rail, divers may explore at their leisure along the beautiful limestone confines of this wonder of nature, confident of their way back to the surface. Penetration beyond the locked gate is with FULL CAVE CERTIFICATION only. Once beyond the gate, cave divers find the need for side mounts. Here you can really feel the 28 million gallons per day water flow. 2004 current maximum recorded depth is 157' with a recorded cave length of 1,642 feet. Growth of this cave penetration continues with the flow of water removing the sand slowly 24/7. Exactly where the water source is, remains the mystery since there is no "spot" where the sand reveals the incoming water flow.