Y Combinator is pretty direct in their statement that without a technical co-founder you will not be accepted into their program. I don’t know about the other accelerators.
Every company is different. Not all start-ups have a huge technology component. In these start-ups a technical co-founder may not be critical.
If the product is a software application, as is the case with nderground, you need a technical founder who will drive the implementation and architecture. Early on, it’s all about technology and product design.