Quoted:

#Copy all necessary lib files etc.
%if 0%{?el5}%{?el6}
install -p -D -m 0755 %{S:1} %{buildroot}%{_initrddir}/rabbitmq-server
%else
install -p -D -m 0755 %{S:6} %{buildroot}%{_unitdir}/%{name}.service
%endif

install -p -D -m 0755 %{S:6} %{buildroot}%{_unitdir}/%{name}.service

should be 

install -p -D -m 0644 %{S:6} %{buildroot}%{_unitdir}/%{name}.service

as there is no need to set it as 755.