[pkscout]

Any ideas why the Artist SlideShow add-on might be picking up incorrect artists from HTBackDrops

htbackdrops uses a name based searching mechanism, so every once in while you will get images for the wrong artist. Unfortunately there isn't anything that can be done about that (at least as far as I can tell).

And I wasn't sure if my local fanart was being picked up by the Artist SlideShow either?

I'd suggest setting AS to use local images first and then turn off all the download sites. Start with a clean AS cache folder and then play an artist you know has local images and see what happens.