I havent seen your mats, but i do have quite a bit of understanding regarding copyright (both for the musical and gfx side). Youre on the safe side, as you did render out textures mapped on a sphere, which can be considered an artwork, period. It is not a straight out flat render of the textures, which is what they mentioned (mentioned doesnt mean they can actually sue you for it, as it most probably wouldnt be recogniced as a valid agreement by court). See, they write tons of weird stuff into license agreements, there are usually loads of points in there that would be smashed by courts). For example XSI prohibits me to sell my license, which is illegal business practice in EU, so regardless of what they write, I can sell it and could sue them if they dont allow me to). So take all these lic agreements with a grain of salt.
Even if you decide to keep them down for your own safety, rest assured that you didnt breach anything.
