Found this on the Arch wiki -

.nemo_action files can be used to create menu entries in the pop-up dialog that comes up since these files are read by nemo whenever you right click. You can invoke a script from these .nemo_action files that does your job, similar to what nautilus-actions does.
You can have a look at /usr/share/nemo/actions/sample.nemo_action and /usr/share/nemo/actions/myaction.py to get an idea of how it works. These files have detailed information on what each field in the action files indicates.
You can visit this website for an example.
Edit :
Nemo actions are similar to nautilus actions in content but vary with respect to the extension name.
In nautilus, newly created actions and menus will be stored on the disk as .desktop files.
The nautilus-actions tool, a graphical editor for nautilus actions, will therefore not work with nemo because it looks for .desktop files, not .nemo_action files.
Summary -
Nautilus scripts can be used if invoked by .nemo_action files, just like nautilus action .desktop files did, and these in turn can be adapted for that purpose. nautilus-actions tool is NOT usable for Nemo due to the difference in paths and extension names.