In HoF, does one need higher ranks in certain skills (Bluff, Diplomacy, Hide, Intimidate, Open Lock, Pick Pocket) than in normal difficulty?

Also, what good (in any difficuly) are Move Silently and Search? I didn't know enemies could track you by noise, and I've always found hidden things by holding the ALT key.

I believe NPCs DC don't change in HOF, so no need to go crazy in any one skill. Same as normal, have someone concentrate in the talkie skills, with some backup in front liner. Hide skill does come in handy, can sneak past tough encounter, get to the treasure chest and better weapon, then go back and kill, kill, kill.
Search skill only comes in handy for secret doors I believe.
In HOF, theives skills come into their own. Pick pocket everyone, some interesting stuff out there. Open lock/ disarm trap quite necessary or have plenty of raise dead.

isnt search for finding traps?

Yes it does detect traps and secret doors and secret compartments.

Afaik Hide determines whether or not you are able to hide the first time. Move Silently is used for the rest of the times when it checks if you manage to still remain hidden.
Search is used to find traps. Disable Device for untrapping. Open Lock does what it says :D
Pick Pocket becomes more difficult in HoF iirc.

Pickpocket becomes near useless in HoF as all NPCs get a massive level boost, and PP checks lvl difference between you and the victim or so I heard. other skills are still useful though. And it feels good to master them!