There is a visa for fiancees to join their future spouses in the US. I assume that while you're getting your interview after a year, your spouse received temporary documents allowing them to travel and work.
Now, if you're talking about meeting your future spouse in the US, then yes. They would have needed a visa to be in the country in the 1st place.
Fiancee visas aren't approved overnight. And if you are out of the country and apply for one you can't come here on a temporary visa (like tourist or H-1) as your application for fiancee visa is considered prima facie evidence that you do intend to stay, hence you don't qualify for a temporary visa or visa waver.
OK so I don't see the problem. I'm not trying to be insensitive or anything. I went through the same process. Is it a pain in the bum? Yes. Are the delays way too long? Yes. But at the end of the day, when you start the GC application process you usually get your temporary documents after a few months (it was 2 for me, another comment claims 6, I guess YEMV) and that's it. Then yeah, it's a pain to have to wait a year to have your marriage scrutinized by an immigration agent, but in the mean time, you can work, travel, etc.
My original comment was just wondering how a "immigrant marriage visa" would change anything.
You would have to have already been on a different visa to have been here in the first place and like nraynaud said, it takes time.