The correct delimiter should be ' / '. This is recognised by WMP and Windows Explorer (and some other players like foobar2000). Unfortunatelly not all players recognise artist delimiter.
Windows Explorer and WMP show ';' as delimiter, although they read and write ' / ' as the delimiter.
By the way, it's ' / ', not '/', so not to split bands like AC/DC into two artists 
My way of saving artist is:
ARTIST=Artist1 / Artist2 / Artist3
TITLE=Title feat. FeatArtist1 & FeatArtist2
And for covers:
ARTIST=CoverArtist1 / CoverArtist2
TITLE=Title feat. CoverFeatArtist (OriginalArtist1 & OriginalArtist2 cover)