The NaplesPU System Verilog code, as well as the custom parts of the NaplesPU toolchain, are covered by the 3-clause BSD license. This type of licenses is classified as permissive, as it imposes minimal restrictions on the use and distribution of the code. As a consequence, you should feel pretty comfortable while reusing the NaplesPU code for your own purposes. In particular, you are not required to distribute the source code in case you incorporate and/or modify NaplesPU in your project. You are just required to keep the BSD license notice and copyright information in the covered source files, if you redistribute them in an open form, or reproduce the notice and copyright information separately in a readable form, if you redistributed binary code.
That should save you most licensing headaches!