Why? Why not. Pretty much all Irishmen sing songs from other nations with an Irish accent! :-)
Unless they are taking the p*ss out of the English.

Seriously, though, surely most singers can imitate accents with some accuracy, because of vocal ability and because they listen!

I remember seeing an interview of Lulu where the interviewer asked her about how she came to speak in almost accentless english, rather than her native glaswegian. She said "I have an ear, -obviously..."