I made this video comparing draw vibrato between an unvalved and valved Trochilus harmonica. Aside from note bending, the rich quality of draw vibrato on an unvalved harmonica is one of the reasons I became a 'half-valver" years ago. I feel like the reed interaction adds a rich and expressive quality to draw vibrato.
https://www.youtube.com/watch?v=7Fq_17gV2J8