EF source says: [FONT="]'That' is often used to introduce defining relative clauses when they follow the words [/FONT]something, anything, everything, nothing, all[FONT="] or a superlative. It may be omitted when it is not the subject of the clause.
I don't see how adding "that are" changes the meaning or improves understandability. In general, good style favours the briefer of two equivalent options. In my opinion, therefore, the passage is better with "that are" left out.