As with so much else, skeptical art is on a continuum. On one end there is pure skeptical discussion such as one might find in the skeptical enquirer or, one might argue, scientific publications. On the far other end is art which happens to also encourage critical thinking but doesn't have an agenda. Somewhere between there we transition between art and discourse.
I think I have found a borderline case: the comic Cectic is very much a skeptical comic, but I find that it specifically engages in discourse rather than being ant artful endeavor. However it does use art, it does engage in skeptical activism and one could argue that there is some artistic satire.
Overall I see it as a borderline case, it doesn't clearly fall on either side of the line it sort of sits in the foggy middle.