From the Minecraft EULA: (http://www.minecraft.net/terms)
"Please think carefully before you make any content available, because it will be made public and might even be used by other people in a way you don‘t like."
Basically, all modifications to the game that are put online are subject to the public domain. This allows us to use the mods without direct permission from the creators, but we prefer if they approved. :)
Out of the kindness in our hearts, you're welcome to forums if you are unhappy with the distribution of your mod in our modpack!