Short answer: yes.

The long answer is that, even if OGA explicitly paid you money to create art, we do not (nor will we ever) take possession of the copyright to that art.  This means that you can still license your artwork however you want, to whomever you want.

Let's say, for example, that you create a set of game graphics and release them here on OGA under the CC-BY-SA license.  If someone would like to use and alter your art without sharing it, they are free to contact you and obtain a license to do so.  You are free to charge them for this license.

Now, there are a couple of catches.  While we will take down any artwork of yours that you request we take down (provided you can provide reasonable proof that you're the author of that work, and that we didn't conpensate you for it), that work is already perpetually licensed CC-BY-SA, and anyone who has already downloaded it has the right to continue using and distributing it under that same license.  They do not, however, have the right to license your work to third parties under different terms.

Furthermore, if you have plans to sell your contributed art to third parties, it is highly recommended that you select either CC-BY-SA, the GPL, or some combination of the two, as there is little motivation for a commercial interest to pay you for the privilege of using your art if you've already granted that privelege without requiring them to share.