Yes i think there's no harm in donating blood or organs. but note that they should be donated.
Now let's give a little thought who actually is Amritdhari Sikh and as far as i think Guru Ji made Amritdhari Sikh to serve the community and help in general awareness and work for the welfare and upliftment of the society. An Amritdhari Sikh is a fearless person ("NIRBAU") and does not have any enimity with anybody ("NIRWAIR"). But let us not forget Guru Hargobind Sahib Ji here who gave us the concept of MIRI and PIRI,i.e. SAINT SOILDER. So it's perfectly ok for any Amritdhari Sikh to donate organs or blood because this will in fact help the community and probably save somebody's life and this is all what is the fundamental concept of making an individual an Amritdahri Sikh.