The B757 and 767's are certified to autoland with 25kt x-winds. The airplane and autoland system don't know if it's severe clear outside or 0 visibility.
Now, back to your question. When making an actual CAT II/III approach, we are limited to no more then 10 kt x-wind per our AOM.
If you think about it, unless you have a level 5 T'storm over the airport and driving rain, CAT II/III conditions are normally caused by dense fog. So, generally speaking, you're not going to have strong winds when conducting these types of approaches in the fog.