It can probably be welded, but would more than likely cost you at least half of what a new one would cost.
If it were me, I think I would get in touch with Wilton, and see what they would recommend, or even see if they would give a hell of a discount on a new one. I would think that they would stand behind their vises. I wouldn't get ****** with them, but just explain to them what has happened. If the vise was not abused, you may have some consolation in making some sort of deal with them.
I know that over the years, at our shop, we had quite a few Wilton Bullets. Some of those were tightened down with Driller hammers to get things together or apart. The vises were definitely abused, but we never saw one crack like that.
Keep us informed as to what direction you go with it.