the score is the hash of the data in the block. the same block on two servers will have the same score (important for replication). different blocks have the same odds of having this same score (that is, astronomically low) regardless of whether they're on one or multiple servers.
that doesn't directly address their suitability as UUIDs. it seems like an odd choice to me (certainly it's an expensive way of generating them), although i guess it depends what your application is.
