I've always heard people say タンクさん and ヒーラーさん in speech though, despite the official terms.
I've heard them too (probably slightly more often than the Japanese words), but it was comforting to remember that the official terms were the clearer ones. I also heard アタッカー ("attacker") for the DPS role, which was also very clear.
I even heard the developers use "proc" (I never would have guess that this came from "programmed random occurrence") in an interview. The Japanese word 追加効果 ("additional effect"), which I think was the only term used in the official 2.0 guidebook, is so much clearer!
Those terms became trend with WOW i guess, then when WOW players moved into other MMOs...
Damage Dealer makes more sense than Damage Per Second -.-
I wonder how manyf FFXIV players have previously played WoW or some other MMO. When I first started this game with the beta, it felt like it was every one of them, except me.
If I were more talented at this game I would talk using time-honored Square/FF magic names like "Fira" for "Fire 2" and let the WoW people be confused for once!