There is little evidence that I know of with vomitoxin being a problem in forages or silages. When evaluating feeds for it affect on the animal, vomitoxin's primary affect is feed refusal and a secondary effect on production.
Ruminants are much more tolerant of vomitoxin than are many monogastric species such as swine.
I am unaware of any evidence to support a claim of hepatotoxicity and deaths due to vomitoxin ingestion are very unlikely. While it may be possible to occasionally find vomitoxin in forages, the molds that produce the mycotoxin much prefer grains such as corn. Therefore, it is unusual to find vomitoxin in alfalfa. Studies done at NDSU have shown good tolerance by beef and sheep to grains high in vomatoxin. However, in dairy the tolerance is still regarded with caution.