With the amount of spices I throw into some of my dishes, particularly southern asian ones, I probably couldn't tell you whats in it if you asked!
But good god, raw hamburger and velveeta and salsa? I think you'd find many meat eaters equally disgusted!!! It's not even couched in trappings of fanciness, like steak tartare....velveeta and raw meat? It just sounds like some idiot who a. had not done any cooking in his life and b. was either really drunk or really idiotic.
Generally I would say the burden is on the guest to announce any things they cannot eat. If I know someone is a Muslim or a vegan, I won't serve pork, or animal products respectively, but I don't have guests fill out a form listing religious or allergic incompatibilities with foods upon arrival. If you are a vegetarian, let your host know so they can cater to you. If they still feed you meat then they are bastards, as appears to be the case with the raw beef Rotel-dip. Likewise if you can only eat halal or kashrut meat, or are allergic to peanuts. It is important to let the host know...until then, the burden is on you, after that, the burden is on them.
I don't announce a list of ingredients so I see no problem in not announcing to everyone that a dip contains spam unless there was reason to believe people had religious or health reasons to avoid eating spam.