I did couple low level FATE today and used only the Cure healing NPC's and other players and that did get me highest reward, including the kill credits/exp from most of the killed stuff too. I wasn't in any party and to me it was nice to see I can participate in a FATE like that, just come in, do my thing and leave and not be left out of the rewards. I just hope that in your case it was some uncommon bug or something else that prevented you getting the rewards that will hopefully get fixed.