May I use "Ash Blossom & Joyous Spring" to negate the effects of cards that send from deck to grave, but not in the specific scenario?
You will be able to chain Ash Blossom to the activation of Shaddoll Fusion.

Ash Blossom reads:


  When a card or effect is activated that includes any of these effects (Quick Effect): You can discard this card; negate that effect.


Because Shaddoll Fusion includes the effect to send cards to the graveyard it counts towards being Ash'd. It doesn't matter if you actually have a special summoned monster on your field, simply having that effect in its effect text makes it viable.

Source: https://www.db.yugioh-card.com/yugiohdb/faq_search.action?ope=5&amp;fid=20586&amp;request_locale=ja