By default it isn't necessary because the tips are just normal Monero transactions (everything is done outside nostr, the relays/network doesn't see/know anything about the transaction)
If you choose the other public options...not 100% sure what is going on there, but I remember reading discussion of opening up a new bounty to do verification properly.
Good question though I'm interested in what the answer is too. You should ask retnull on the bounty page to be sure.