diction according to the concise oxford dictionary is wording and phrasing ,verbal style, therefore having an accent is not going to prevent good diction, as has been clerly illustrated by the you tube clips I have put up.
now, good diction is one of the most important techniques for a singer ,you are singing words that need to be understood, if it was a question of singning just beiing a production of a pleasant sound, then it would be acceptable to sing in tune but sing gobbledegook.
One songwriter/singer that always impressed on people how important the words of his songs were ,was woody guthrie, he considered his words and his abilty to coomunicate the most important part of his singing, it was only in his latter years when he was ill , that his diction became less understandable, this was the time that dylan started copying him and mumbling in an affected manner, in his earlier years Guthrie WORDS WERE UNDERSTANDABLE, even though he had an Oakie accent.
jimcarroll , i rest my case, you are completely and utterly wrong,.