Of course you can spray it on fleece. The stuff is harmlessit's all around us these days, in carpets and furnitureand can be used perfectly safely on things you wear. Mind you, what it does is make a fleece jacket stain resistant. It won't make it waterproof. Most outdoor garments already carry a Scotchgard-like material called a durable water repellent (DWR) coating. This helps water bead up and run off, although in time the water will overwhelm the DWR and saturate the garment surface. That will happen pretty quickly in a loosely woven garment such as a fleece jacket.
For what it's worth, Nikwax makes a wash-in material designed for fleece, wool, and similar materialsthat will enhance their water repellency. It's called Nikwax TX-10 Polarproof, and sells for $11 a bottle. Just toss it and the jacket in the laundry, and wash away.