Actually, the roots used in dandelion tea are generally roasted. (I don’t know much about these particular roots although I drink the tea daily, but often when roots are prepared in this way there is a good reason for it so I’d suggest doing more checking on that topic.) However, dried leaves and flowers can also be used in a variety of ways including teas. I can’t see why you couldn’t dry the leaves (must admit I’d do it the traditional way, hanging tied in bunches and/or in a paper bag rather than use all the eletric energy dehydrating), all that said my personal concern would be whether or not my rabbits would be interested in eating them. I have offered dried herbs and leaves with mixed results. Herbs they enjoy fresh do not interest them dry, but blackberry, raspberry and currant leaves they enjoy both dry and fresh. Since they do all have different preferences you may want to check with them before going through a lot of bother prepping a plant they may reject. And dried leaves can supplement but can never replace fresh greens in a healthy diet for a rabbit.