Well it is a massive problem to me, my Aperture library is over 100GB, and I can't be dealing with my computer whirring away all night backing that up on a daily basis. Is that what it would do?
Well if you made any changes to it yes. I see where you are coming from (my library is much less than yours so it's not an issue for me personally). In your case I would tell TM to ignore your library and then use the Vault.