Would that be vee-o-la or vie-o-la? I like the Veeola version - like the musical instrument, not like the flower. And I much prefer it to Violet, which I really dislike.
I taught a Viola once: typical bubbly schoolgirl, cheerful and friendly, learning the drums! Face like a beautiful tragic mask, which all the art students queued up to draw, but she was perfectly happy as a person. I wouldn't use the name myself, but it's got good associations.