<< how does FSB overclocking affect the IDE bus? >>
Depending on the chipset and motherboard, certain fsb settings will cause the PCI and AGP busses to run out of spec. The IDE bus is run off the PCI bus (on modern motherboards)
<< does o/c cause its speed to run out of spec? >>
In the majority of cases.
<< is the effect the same as the effect on a HDD running off of a PCI IDE controller card? >>
Yes.
<< and does it apply to HDDs connected to onboard RAID? >>
Yes.