Yes! NaNoWriMo, Camp NaNoWriMo, and NaNoWriMo's Young Writers Program are projects of National Novel Writing Month, a 501(c)(3) nonprofit organization based in Berkeley, California. All donations are fully tax-deductible in the United States.
If you are donating from outside the United States, we recommend you check with the relevant authority in your country about whether or not donations to NaNoWriMo are tax-deductible.