The essential principles of open-sourcing hardware and software remain the same: primarily, to ensure everyone has the right to use and reuse what you've created.
You do, however, need to pick (or make - though that's not recommended) a license that will apply well to both software and hardware. Hardware has the difference of being rather, well, physical, and as such has different considerations to note. Specifically, there are two parts to the hardware: the documents you used to create it, and the product itself.
As with all licensing, consider what you want users to be able to do with what you've made. If you're licensing so that people can modify and redistribute your software, do you want them hacking away at your hardware too and redistributing that? There's a different type and level of effort in creating hardware and software: are you more protective of one than the other?
tl;dr: There's nothing stopping you, but consider what you want to happen with your creation.