It's totally safe to flash LEDE snapshots on the HG566a, either by installing via CFE bootloader web interface or upgrading via Openwrt/LEDE itself.
Upgrading via Openwrt/LEDE is always totally safe.
Upgrading via CFE an Openwrt snapshot could brick the router (only recoverable via JTAG). It turns out that the bootloader modified by Huawei can destroy itself if you use a bad firmware, with bad info in the header for flashing on the first block (where the bootloader lives).