I love cranning on open strings on fiddle. D and A crans are good, but I even do it on the open E string as well. I also do sometimes do a proper roll on an A (and even, rarely a D) by playing it on the D string with a second finger. Ususally, in that case, I would play it simultaneously with sounding the open A string.
Not that any of that helps with whistle. Um, but I do roll the C# sometimes on whistle. I’m not wrong to do this, am I? Well, I don’t care. I like it. I roll the middle D as well, even though Mr Guru Sir has told me I can’t. 