Just in : Saw an HTML designer writing professional "coder" in his resumé. Can HTML(and CSS) designers be considered coders?

No...if being able to switch on computer make U a Developer perhaps rules of who's coder or not might change

Professional "coder" is a shitty term in general. Web developer would be better

As of my knowledge neither HTML nor CSS are PROGRAMMING languages. So no coder, but a designer?

How about Less and Sass?

Well in general HTML and CSS isn't considered to be programming languages Like some others..

However.. someone Who can make very good looking responsive websites do deserve some credit as they need to be aware of all elements in the HTML and style them with "code". HTML and CSS does not contain functions and such. Once you get to javascript, Then we can start to talk code :)

Front end developer.