I have Minecraft Forge 1.8, and I was wondering if 1.8.1 mods will work with Forge 1.8.
Most mods should work because there were no massive changes to the Forge API between 1.8-1.8.1.
We have released a new version of Minecraft, 1.8.1, which brings a bunch of new optimizations and bug fixes. It’s 100% compatible with 1.8, and comes with extra hugs.
Mods would only break if they use a system with one of those fixes
No. They are different versions, and, as a result, you will not be able to. This is because when you use Forge 1.8, you are in fact using a modded version of 1.8. As a result, a 1.8.1 is incompatible, because it is designed to run with a different version of MineCraft.