I have never heard of using a vise to make harnesses so started looking around YouTube and found this......
[video=youtube]
Makes all the sense in the world to me know, great way to make it simple especially for keeping distance between hooks consistent. I've only ever used harnesses with 2 hooks though.
As for a vise to mainly do this, any non-rotating vise would do. Thompson Model A style is about as simple as you can get. But as the video shows, you might want something that the angle can be pointed vertical. Not sure what vise is used in the video......... i have it muted here at work.
Maybe get a dirt cheap vise and a separate vise that has a few more bells and whistles to do both hooks of a harness and use the better to tie jigs/flies on?