Think this somewhat mirrors a discussion around here from way back. Personally? I can draw a clear, comfortable line between artist and product. There's a reason we're compelled in school to address narrative intent rather than authorial intent. Once released into the world, the product has a life of its own, and a will that may defy its creator. As a critic, you address the character of the work, and leave that of the author to the biographers. Lucky for us, Hitler's paintings were mall-grade trash, so we don't have to worry too much about it. But if his shit popped? Why not appreciate it on its own grounds?
I don't think I've ever checked out his paintings before, or if I did I have forgotten them. A quick search and I find that they're not awful, but they aren't anything special either.