We are thinking of purchasing a Eurail Pass, however I have seen that some trains in Italy (Italo) do not use it. We need to take a sleeper train from Venice to Munich. Is this possible with the Eurail Pass?
You may want to read this before deciding if a Eurail Pass is worth it for you, you may save money buying point- to- point tickets in advance: http://tinyurl.com/Rail-pass-vs-point-to-point
A Eurail Pass will get a seat when you pay a supplement, but if you want sleeping accommodations, you will pay the same or more than others buying advance purchase tickets.
German Rail DB Bahn operates City Night Line sleeper train from Venice to Munich.
http://www.bahn.com/citynightline/view/en/service/komfortklassen/schlafwagen/uebersicht_en.shtml
A supplement is payable for your sleeper seat/couchette/compartment.
Trains that don't accept rail passes are still very much the exception (and the Paris-Italy night train is one of those exceptions), not the rule. The Venice-Munich night train offers a standard range of sleeper fees to use together with a rail pass. See also:
Sleeping on trains: http://www.ricksteves.com/travel-tips/transportation/trains/night-trains
Seat reservations: http://www.ricksteves.com/travel-tips/transportation/trains/reservations
Reservation costs per train route (info from about 2013): http://euraide.arsdehnel.net/docs/trains/pdf/train358.pdf