hmm like title say why not?
on the official wiki from forestry it say:
License
The code of “Forestry for Minecraft” in source or binary form is the intellectual property of SirSengir. You may not reproduce, redistribute or modify it unless noted otherwise below.
Mod Packs: You are free to add Forestry to your modpack and redistribute it, as long as the modpack is strictly non-profit and none of the other mods are included against their license. Yes, this even applies to packs made by people I don't like. Don't expect me to play tech support for your modpack though. (Applies to 2.0.0.6+ and later.)