This is the reason why I dont dare to render my models and textures in such game engines. The risk is simply too high.
I don't think just rendering your models in their engine for showcase gives them all the rights over your work, that's not possible... It's probably only when you would make an actual MOD (and it's not true for every engine out there, Unreal 3 engine does not have such a license afaik).
Also, if MOD teams use 3rd party model packs like yours, it won't be automatically be property of the engine creators either for sure.
