I wouldn't bother. The amount you can earn from these campaigns are quite small, even for Legendary ranks.
That's right. If to cash out by little like 50-100$ a month a bank won't has any pretensions to those money. Taxation is more about big sum of money which source you should represent to the bank and taxation system.
In many of the countries, there is a limit after which the income is taxable. For example, here in India you can show income up to Rs. 50,000 as gift from strangers. After that amount, you need to pay taxes on the additional amount.