If you click on Special Travel Bonuses on this page: http://www.raileurope.com/us/rail/passes/eurail_flexipass.htm another window will open with this info:

Greece a.. When your pass is valid in Greece and Italy, free ferry crossing from Patras, Igoumenitsa and Corfu to Brindisi (Italy) operated by HML (Hellenic Mediterranean Lines) and Blue Star Ferries. In July and August, a 20 euro high season surcharge must be paid. Port taxes are extra. b.. When your pass is valid in Greece and Italy, free ferry crossings from Patras and Igoumenitsa to Ancona and Bari (Italy) operated by 'Superfast Ferries'. In July and August, the equivalent of 20 euro high season surcharge must be paid. Port taxes are extra. c.. 25% reduction on a one-day-cruise from Athens to the isles of Aegina, Poros and Hydra, operated by Ionian Travel. For reservations: (+30) 1 523-9609.

Other bonuses Free and reduced transportation Eurail Pass holders are entitled to a variety of bonuses besides the shipping lines we've mentioned above.

Only the following companies will honor your Pass. Arrange your free or discount travel locally, and always confirm that the company you are dealing with actually honors the bonus discount.

Holders of a Eurailpass Flexi, or a Eurail Selectpass note that a free transportation bonus requires use of a travel day; reduction bonuses do not require use of a travel day.

a.. 15 % reduction on certain hotels in Athens. For information: Ionian Travel at (+30) 1 523 9609

I think you may assume that a validated travel pass would be a requirement for any of these bonuses.

Regards, Linda