Forklift truck drivers and hearing protection
Unless they are prone to wearing red y-fronts outside their blue spandex leggings and flying off to assist damsels in distress at a moment's notice so are invincible to the effects of excess noise, then the short answer is YES, they do have to wear hearing protection as the noise will have the same impact on them as on any other person.
If a FLT (Forklift truck) driver routinely goes into a high noise area to the extent that their daily exposure is exceeding 85dB(A) then they are at risk of noise induced hearing loss. This means that over time their hearing may start to deteriorate through the effects of the exposures and they will eventually no longer be able to hear the screams of their victims as they run them over anyway, even without hearing protection.
FLT drivers should be looked at closely though as it is particularly important that they are not provided with too much protection, i.e. hearing protection that is blocking out too much external noise. What they need is a protector which is getting them down to about say 77 or 78dB under the protector so they are safe from possible hearing loss but also still able to hear what is going on around them at a decent level.
Or provide a FLT with an enclosed cab that reduces the noise to a safe level without hearing protection.
One exception which may apply
The Noise Regs say that hearing protection is needed by those who have a noise exposure which is routinely exceeding 85dB(A). The Regs also then say that areas where this happens should be marked with the blue and white signs as mandatory hearing protection zones. That is actually rather contradictory as one is saying it is time-based while the other is saying it is location-based and this could come into play with our FLT driver...
Assume you have an area where employees are routinely exposed to 88dB(A) so it is signed as a mandatory hearing protection area. Your FLT driver meanwhile largely works in the very quiet stores area and only occasionally goes into the higher noise level work area, maybe for up to an hour a day in total. In this case, the FLT driver's noise exposure will not come close to the 85dB(A) limit so technically, according to the Regs hearing protection is not needed, even though another part of the Regs say the zone must be signed as a mandatory hearing protection area for anyone in there. If you could guarantee that the FLT driver never ever spends long enough in the high noise area to breach the 85dB(A) limit then there is an argument that hearing protection is not needed, but this is based on noise exposure duration rather than a blanket exemption due to the fact they are a FLT driver and would apply equally to a pedestrian as it would a FLT driver. This could be covered in the noise risk assessment for you but if in doubt as to the duration of any possible FLT driver noise exposures, stick to the principle of hearing protection being needed in all areas zoned as having high noise levels.