Yes, though sharing BLE with other protocols is challenging (even with first-class citizens like ANT+ there are various caveats). The proprietary protocols are Shockburst/Gazelle [0] which are based of the ancient nrf24 setup.
Having said that, the radio peripheral on the chip is dead simple to drive bare-metal. Create a packet (with the convenience function), put its address in a register and hit the 'send' bit (more or less, glossing over waiting for ready bits here). Receiving is as easy - point to where you want packets to land, go into RX mode and wait for the "packet received" bit to be set.
