Yes, if you consider dark art to be "anything that would fall under the horror category in film", which I do. That includes dark psychological, gore, dark themes, some forms of black comedy - all of which I think you've done to some extent.
I would say yes because of some of the themes and tones--I don't think color and brightness should be a determining factor on whether something is 'dark' or not. It just tends to go hand in hand most of the time. I think many people also tend to associate 'dark' with 'evil/bad' or horror, which I think largely isn't the case. You take things people don't always like to talk about and make it more approachable, unavoidable, or easier to associate with, I think, which to me is a large factor of what makes something dark
To me real "dark art" or even stories aren't necessarily overly graphic with a lot of gore, or something with a lot of black or dark colors. For me "dark" is something more, where you get the feeling that something more is underneth the surface, perhaps twisted. It's all about presentation and emotion.
Your art and characters always have this feeling of something more complex and not completely pleasent beneath the surface.
So yes, but I do think that "dark" alone doesn't adequately describe your work, simply because the word "dark" is often just slapped on a picture because there is a little gore, or the person in it is wearing black lipstick.
Off topic question.... do you ever take comissons?