One way to deal with them: if you have some software package you only want to build as quick as possible and don't want to bother with any nix stuff, spawn an Ubuntu (or any other distro if the package has instructions for a certain distro) docker container and build the app within that. (Or use steam-run from NixOS which is basically an Ubuntu container)

This also has the advantage that you can use the exact same distribution that the instructions for said package mention. (If the thing you want to compile has instructions for Ubuntu 16.04 no problem just use the docker image for that)

For anything that you want to use on a regular basis, creating a nix package is pretty easy most of the time. If you only want to build a newer version of a package directly from git, you can even copy the package for the stable version and just overwrite the src in many cases.

Regarding software that works on NixOS but not on other distros I think it's usually the other way around: by testing your software on NixOS you uncover issues that would have made your software less portable (hidden dependencies, hardcoded path assumptions, ...)