It is not wrong to say Ramanuja-dasa while doing abhivadanam but the austerities are based upon one’s gothram, suthram, shakai, and vedam upon which rituals like sandhyavandanam, vivham, upanayanam, seemantham are based; accordingly, this includes avani avittam. Hence one must know their gothram, suthram and should never forget them. Those who belong to their respective gothram and suthram must utter the respective name of the sages (all the sages (rishis) are pious vaishnavas) mentioning Ramanuja-Dasa along with. If we leave this out, we shall loose the austerities starting from sandhyavandanam, yagnopavitham etc.
The term Ramanujadasa is tradition-based while Abhivadanam is Vaidika-based, there are no contradictions between these, we cannot say one will do because both are required.