It's become an informal consensus among WP:BASEBALL editors (though it's not yet written into WP:NSPORTS, I'll propose it) that we should consider college baseball First Team All-Americans to be notable. In the three cases I'm working on today (Martin, Michael Roth (baseball) and Jason Krizan), they seem to meet GNG. The individuals on those minor league prospect pages generally don't have the same level of notability, though I'm sure some of them do deserve their own pages already. –