I totally understand your viewpoint.
It is not leeching indeed
However it is affecting someone elses gameplay and EU experience. If this is against his will, and interfering with other people's EU experience is against the TOU.
I have nothing against healing people. I often heal people who I see are in need. But I do that for fun and to help out. Not to get their loot.
The shared mob being divided against shooters is the intended feature of shared mob events. The fappers loot is a silly coincidence.
Claiming this is a TOU violation is taking this to an extreme level. Using your example I could accuse people of ruining my experience just for hunting in the same area I am.
Realistically though, you would lose more from taking the time to stop firing, equip your fap, heal, re-equip your weapon and begin firing again than if some healed you. The IMK2 for example costs a base 15.255 pec per shot and at 60 shots a minute would pump 9.153 ped into a mob per min. Someone using a modified Omegaton FAP would be spending 1 pec per heal and at 30 heals per minute could do a maximum of .3 ped healing in that same minute. 3.29% of the loot 'pool' maximum if ONLY you were killing it. If you NEEDED that much healing you really shouldn't be doing that mob as you'd never heal yourself that much.