I don't think the violinist comparison is fair.

Any violinist worth their salt has practiced sight reading to death. Absolute death. It's difficult to do, yes, but if you're playing in any sort of group situation (orchestra, etc), sight reading is extremely important.

Unless you're saying "I drew some lines on this piece of paper that represent the strings on the violin; I want you to play the piece of paper like you would the instrument." In which case it's a worthless interview. Whiteboards are fairly common for code snippits and pseudocode at most of the jobs I've worked. Pieces of paper with representational lines for the strings are used as individual studies (e.g., sheet music) - not for collaboration. That's usually done in jam-format..