The short answer: of course they are! The longer answer? Possibly, see more.
The simple approach would be to take definition of art and then see if role-playing games fit that definition. The problem with this approach is that there is no single definition of art. Depending on the choice of definition role-playing games could end up being art or not being art. Of course it would be uplifting to find a definition that would allow us to call role-playing games art, but there is another way which could be better in answering the question.
Aaron Smuts asks the same question about video games. (The answer is, by the way, yes.) His approach is to take several major ways of defining art and seeing if video games fulfill the criteria set by these definitions. If we consider role-playing games to be games, then his answer should then cover also role-playing games. But it is not entirely self-evident that role-playing games are games (see for example Jesper Juul why role-playing games are not “full-case games”). Regardless if role-playing games are games, we could use Smuts’ approach and test if role-playing games fulfill the criteria set for art. The theories by which he tests are made apparent by the following quote:
I offer reasons for thinking that video games can be art according to historical, aesthetic, institutional, representational and expressive theories of art. If we can agree that all these theories generally track our intuitions about what should be considered art, then when they are all in agreement we have good reason to think that we have successfully picked out an art form.
The criteria are quite demanding, seeing that role-playing games would have to fulfill the demands of five different theories of art to be able to qualify. I’m not yet sure if they can do that. Regardless if the answer is yes or no, the answer will be quite long, which is why I will not try to answer it here. It will be a topic for another post, or five.
Note that even if the answer turns out to be yes, it doesn’t mean that every role-playing game ever played or published is art, just like saying that visual art is art does not mean that every picture ever drawn is art. It just means that role-playing games have the potential to be art and that there probably are some role-playing games that could (or should) be considered works of art.