Yes, other male dogs can tell if a dog is not neutered. An intact dog is not always more agressive, but there is a greater likelyhood, all other things being equal. Some breeds don't exhibit the behavior. I had a male unneutered Australian Terrier a few years ago (a Champion Stud dog), and ANY male dog he came in contact with was fair game, no matter how much larger the dog was. Most Terriers are that way, and serious breeders cannot generally keep more than one stud dog at a time. The other dogs can definitely smell the hormones in the urine when they mark territory. My current Australian Terrier is neutered, but he still stiffens up around other males...he and my male rescue dog had some issues at first, but once Rider, the Terrier, established dominance (over everybody, except me), they get along fine now.
Large breeds are not for everyone...some are very willfull and the owner must always establish him/herself as Alpha or there will be trouble at some point in time.
Zeus sounds like a good dog...and Dalmations are not for everyone either. People who buy/own breeds should do more research on their temperment and fully understand what they are getting when that cute puppy grows up. Mostly it's the owner's fault if the dog exhibits bad behavior. Ear and tail position tells a lot...