Practically speaking, are special tools needed to remove the viscous fan

technically yes if the the threads are corroded/overtight, there is a factory tool to hold the pulley as you loosen the vuscous coupling. In reality Techs just use a thin fan wrench and a short sharp shock with a hammer will break it loose. Bear in mind that this is a learned technique and viscous couplings have both LH and RH threads depending on application. (hint the coupling should be being tightened with the engine running and the crank turns in a clockwise direction!) Havefun