Actually, there is a dedicated “Featured Artist” Main Performer credit and it is far more appropriate to use this. You can do this in Roon via credit editing, but you can also use the PERSONNEL tag in your files. The contents of such a tag would be:
<featured_artist_name> - Featured Artist
And you can have multiple lines/credits in a PERSONNEL tag.
In general, our advice is to concentrate on getting the information into Roon as accurately as possible; then we can present it as best we can.