Tees - the classic VRS setup starts with you in a OGE hover which implies rather high pitch settings - you don't have to lower the lever very much at all to induce a RoD so your pitch setting are still high. Then when you raise the lever to arrest the RoD your pitch settings are higher than they were in the hover - now you have a powerful tip vortex and very high AoA at the root, a RoD, low IAS and power applied - all the ingredients required!
In an updraught you already have lower pitch settings to maintain the hover and the only danger is the variable nature of the updraught - if you don't react quickly enough to it reducing then you may well find your self with a RoD you didn't want and have to apply a lot of power to arrest it - in this case you are in a similar situation to the normal free air hover and VRS could ensue.