I think that where many people get themselves into trouble is in trying to reproduce accents with more fidelity than they can pull off.

For example, if an American has a good grasp of the basic attributes of Scots pronunciation (e.g., vowels, intonation) I see nothing wrong with using this knowledge in singing Scottish material; in fact, I can't imagine trying to sing a Scots song in most US regional accents.

On the flip side, using distinctive features from both Glasgow and Skye at once--or worse, Glasgow and Belfast--would be humorous at best, to anyone who knows the difference. (Two cents' worth from a Canadian of Scots extraction.)