Look at the denim theme in Geeklog 2.1.1. In the functions.php you can see how the css and javascript files are added for uikit.
Right now the denim theme doesn't use uikit a whole lot but that will change for Geeklog 2.1.2 where Dengen has been hard at work updating the denim theme to use a lot more of the styles and features uikit offers.