if u have bootmii as boot2 and a nand backup, u are brick proof (with the exception of a ninty boot2 update, which uninstalled bootmii as boot2, but if this happens, u can reinstall bootmii as boot2 and again be brick proof)
if u have bootmii as boot2, then priiloader isn't required for brick protection, but it allows u to use system menu hacks (also available via start patch) and allow you to customize how you wii boots up (ie. to system menu, or to CFG loader, or to a crazy intro, or crazy intro video etc.)