I never remember how to do this, if you need vendor specific bits inside a spec file (like init scripts etc) you can use this to do different things depending on vendor.

%if "%{_vendor}" == "suse"
  # Suse specific stuff
%endif
%if "%{_vendor}" == "redhat"
  # Redhat specific stuff
%endif

If…else works like this:

%if "%{vendor}" == "suse"
  # Suse specific stuff
%else
  # Redhat specific stuff
%endif