If that’s the case, we misinterpreted what you meant with your previous question, sorry about that.
You are absolutely allowed to decide that you don’t want to work with NSFW, whether that is by not drawing it yourself, or avoiding works rated M or E altogether. (if you want to avoid NSFW content within the server as well, that is also possible, since those topics have been given their own channels).
The way matching works is that an artist picks—depending on what the total number of participants will be this year—10 or 15 of the fics they would be willing to illustrate for, and they will be assigned to one of their chosen fics. By avoiding picking fics which have indicated that they will contain NSFW content, you will never be assigned to those. NSFW fics are not usually the majority, so they are easy to avoid if that’s what you wish.
Once matched, you are then allowed to choose what you’d like to draw, and it is entirely up to you how/what you make, so long as it is connected to your writer’s fic. You won’t ever be forced to draw something you don’t want to.