Sometimes they're nice to have but it's not hard to get by without a tail vise. I did without one for three or four years and now that I have one I don't use it all that much. Here's how I would lay out the top of a 60" split-top workbench if I was building one without the tail vise.
After a student showed me how he used them, the row of dog holes along the front edge of the bench have become a regular part of my work holding strategy. You don't need nearly as many as you do with a Tail vise. I think six or seven inches apart would work best. I also moved them back from the edge a little bit. When you use them with a tail vise it's helpful to have them closer to the front, especially if you use moulding or joinery planes with fences.
If you're planning to build a solid slab top, you can start with this drawing and adjust it to the final depth of your bench. Then move the center row of dog holes so that they are half way between the front row and the back row.