As long as you're honest about your activities and your skill level, why not?
I say honest because I know a pre-dent who put "piano" as one of her hobbies but she hadn't touched a piano since she was seven and taking lessons. She got into dental school, but how embarrassing would it be if someone asked for a demonstration?
Clearly they list hobbies as something to include, so if you paint enough to call it a hobby, go for it.
I put a more general "Arts and Crafts" listing on mine because every week I try to complete a small creative project- whether that's painting, sewing, making jewelry, refurbishing furniture, etc.
Also, I put "Insect Collecting" and explained how I learned to properly collect and preserve entomological specimens in class but how I continue to collect them on an amateur basis... to decorate my home. (Basically, I've been robbing campus of its pollinators the last few springs.)
Of course any club you're part of should go there. Also any volunteer activities that are "non-animal" in nature. Honestly, that section is really just a hodge-podge of left-over activities.