We have a good mix of fixed wing (up to B767 size) and helicopters of all sizes (Offshore, training, Police, Helimed and private - just about the whole spectrum).
Vortex wake is strictly applied to all helicopters, the same as if they were fixed wing a/c, (this is not just an Airport Authority requirement, but also from the UK CAA), so much so that if the Police or Helimed have called for start or are ready for taxy, other departures will be delayed to ensure that they're not affected.
I don't know who told you otherwise, but helicopters in the hover or air taxying are just as vunerable to vortex wake.
There is a current Eurocontrol project on the subject of vortex wake, the main thrust of which is to establish the crosswind and/or component at which vortex wake need not be applied.
The general rule of thumb in the UK Military is, (I think), if the wind is greater than 10kt and the preceeding a/c is not a "Heavy", then V/W is not applied and I think that's the sort of minima Eurocontrol are hoping to prove is safe.
Unfortunately I don't have a reference for you.