Can you turn a video of a silhouetted person into a shape layer

The easiest thing to do would be to generate a simple silhouette copy of your dancer by keying or color controls, or even rotoscope, pre-compose moving all attributes, then use Layer/Create/Mask from Layer. When you get to that point make sure Preview is turned on, then simplify the path as much as possible. 

When you get that far, select the mask path with all its keyframes, start a new shape layer with no fill and a stroke using the pen, move to the first frame of the comp, click anywhere in the new shape layer with the pen, and paste. 

Repeat for every path in the created layer. Hopefully, there is only one or two of them. 

When that is done, use the Add: Offset Paths tool in the shape layer and create as many outlines as you want. As long as the path isn't too complex, this should render fairly quickly.

One more workflow suggestion: Pre-edit your dancer footage, make sure each shot you use is short and clean and create a new comp for each shot. The average shot in my edited movies is less than 7 seconds, so almost all of my AE comps are seven seconds or less. I render production masters from each comp and do the final editing in my NLE. 

You can copy & paste mask paths to shape paths. The auto-trace will just make them complex, so you may run into issues with performance as well as consistency of the shape.

Mylenium 

It's gonna be a time suck no matter what method you use. Repeating complex contours is a whole different thing than simple patterns. That aside there's a million ways to create outlines from applying a stroke layer style to doing an auto-trace to create a mask path. The repetitions can then be created with the Echo effect, alternate "video feedback" effects or using shape layer repeaters. Point in case: It's doable, but will require some work and patience.

Mylenium