I flew Lufthansa multiple times with a Giant Kennel ( 48" Petmate Vari Ultra, link) and never had any issues with getting it accepted in either North America or Europe. A friend who is in the Canadian military used them to move from Canada to Italy on military orders just last month, he had the same kennel that you have for his Golden Retriever and there were no issues.

Unfortunately, Delta indeed is not an option for you. Their ATL-VCE nonstop uses B767 aircraft. Delta stopped accepting animals in the hold on 767s in 2012: Delta does not accept animals as checked baggage or cargo on any Delta operated B767 aircraft systemwide. There are no exceptions to this restriction for any customers, including military customers.

AA is out as well although their crate policies allow your size (max. dimensions on AA are 48" L x 32" W x 35" H). The A330s they fly to Venice only allow up to medium sized crates. If you wanted to fly AA with a large dog in the hold, you'd have to fly them to Milan which is served by 777s out of MIA and JFK - giant crates are OK on those flights - and drive the rest of the way (two-and-a-half hours, 150 miles). The issue here is finding a domestic connection to either JFK or MIA that's operated by aircraft that'll take large crates. Out of personal experience, as schedules constantly change and aircraft get substituted, that can be a daunting task and is nothing I`d recommend to an inexperienced traveller.