a [graffiti] tagger only tags.
graff is really diffrent then gallery art, and 'graffiti artist' suggests too much similarity imho.
so 'writer', or 'graffiti writer', is the best. its also the most used word inside the community.
scrachiti is just another form of tagging, so it doesnt have any special names.

im a graff writer.. and i just bumped into this site surfing. thought i'd help you out.