In my experience it is incredibly hard to align incentives in vendor client relationships.
Ideally we all want to optimize for speed, quality and cost. But in reality you can only optimize for two qualities at the same time .
Unless you are choosing a top billing firm like Pivotal labs, its is very likely that the outsourcing firm you pick is working with mid tier talent at best.
That being said, outsourced teams can be great in getting hacking together a proof of concept.
I have rarely seen hands off approach work for early stage products. An effective approach would be to have someone technical on your team that is savvy enough to communicate, drive and manage the outsourced development on daily basis.
As you see traction you will have to take the call on developing your own talent or investing in developing the talent of an outsourced partner.
I am biased towards building my own teams however i have known entrepreneurs who have done fairly well with outsourced teams.