You can play it, and there's no risk because your updates are blocked. Even if your wii bricks, you got priiloader, and this can like "revive" your wii.
Erm...partially yes. But not quite. And it's not priiloader itself that does any reviving.
Priiloader can be loaded instead of the wii menu (by holding the reset button while powering on the wii). As such, you MAY gain entrance to the HBC and fix whatever caused your wii to brick in the first place (eg. a bad system menu theme or installed wad with a faulty channel). Or if you have bootmii installed as an IOS, you can use priiloader to run it in case of a brick (it's actually bootmii that's the standard backup/restore program on the wii...priiloader is just a means to access it).
But it can't help everything. If you delete the wrong IOS'es, priiloader won't boot. So a bit of cautiousness is still advised.
(not that there's ANY reason to go out and delete IOS'es...but that aside).
But on topic: I can testify: the block disc updates does exactly that: it skips updates that are on the disc and goes directly into playing the game. And the worst that can happen if you play a game with outdated IOS'es is that the game crashes. It won't brick it (in other words: the chances of not being able to turn on your wii afterwards are so slim they're pretty much zero).