This isn't as clearcut as you might imagine. Or rather, it is pretty clearcut, but in the opposite direction than you are framing your question. First, as far as D&D goes, roll20 has a licensing agreement with WOTC. They publish several licensed WotC products, so obviously WotC must endorse roll20's use of D&D character sheets. They are after all needed for the use of those officially license products. Secondly, there's a long tradition in the rpg industry of game publishers unofficially and sometimes officially allowing fan creations of things like character sheets. Partly this is due to the fact the rpg games industry is actually pretty small - there's very few companies could actually afford to legally pursue even a fraction of the fan creators of character sheets, and the bad publicity would be crippling. Also, there is the question of what is actually legally enforceable. The fact is, game rules are not subject to copyright law. You can't copyright a set of rules, you can only copyright a specific expression of those rules. While various licenses have sprung up around games since the D&D3e OGL was created, in fact these licenses are more restrictive than what is allowed by copyright law, and people don't have to use them to do a lot of things - like creating character sheets of their own. And of course, the specific Character Sheets that companies have created are not competing products with the the roll20 character sheets. You can't use roll20 sheets outside of roll20, and you can't use other publisher's sheets inside roll20. The usage is different, they don't compete. It's important to remember that companies like to create licenses to maintain control over their properties, but those licenses only carry wait when people agree to use them. Copyright law itself is much more permissive.
