Read the forums ToS, it's probably in there that they can use whatever you write for their own purpose.
Is it ethical, yes, should they cite you as a reference, yes.
Here's something possibly interesting. I'm toying with the idea of creating a total mod to a game based around Games Workshop's Mordheim franchise. I was reading the legal section of their site earlier, and stumbled across something interesting.
Any notes, e-mails, online messages or bulletin board postings, ideas, suggestions, concepts, designs, or other material submitted to any physical GW company address or to any web site owned or controlled by GW and/or to any e-mail addresses contained in or on those web sites ("GW Web Sites") will become the property of GW throughout the world and GW shall be entitled to use the material for any type of use forever, including in any media whether now known or hereafter devised. When you submit any material to any physical GW company address or any GW Web Sites, you agree, offer, warrant, and represent, both explicitly and tacitly (and GW accepts) that you are assigning all intellectual property rights in that material to GW and that GW has the right to use that material at any time entirely in its own discretion for whatsoever purpose including for commercial, promotional, and advertising purposes without any obligation (including any financial obligation) to you now or at any time in the future. You waive and relinquish any rights, including "moral rights," that may exist in any content to the furthest extent permissible by law and agree not to assert any rights over that content. We are afraid that in order to protect ourselves legally, this is the only way we can operate. If you are unhappy with this policy, then please do not post or send any material to GW.