If it went the volunteer route then characters would probably have some idea they were being brought to help and how difficult it might be for them. Otherwise I think the format of the game and how it would translate allows room for characters to learn to be decent Guardians. We all start out at level 1 and work our way up to 40, after all, and I imagine from the popularity of similar elements in CDC and Eachdraidh that that progression would be a core interest for players in the game.

I would personally put in an age limit for characters though. Probably 16 rather than 18 just to remove the chance of smaller children trying to get around, but still allow for teen drama/shounen types who probably would adapt just fine.