Short answer, yes.

Long answer, you can keep the existing work in package deployment and new work in Project deployment. We are doing the same thing where I'm at now. All our existing packages are actually being kept in 2008 R2 and new work is being done in 2012. If/when we migrate the 2008 R2 packages to 2012/2014 we'll evaluate them on a case by case basis and decide how to handle each one.