The problem with this tactic of scanning for targets while hovering behind trees is two fold.
Not only can any modern PESA ground based SAM radar track such targets, since to hover in 10-30m altitude means that you are not further than 4km away from the SAM/SHORAD, which means you are as clear as a dying star at a night sky, despite trees being some source of clutter reflection, but the background is still the Sky a very poor environment of clutter and reflections of radar waves, aswell rotor blades have a very high amount of radar wave reflection aswell they are easily distinguishable from most sources, since they turn and have constantly a changing angle and surface they reflect the radars back, which every SAM radar can track and recognize as a source of artificial object and not a clutter.
That was the first problem, very short range, highl RCS since radar and rotor blades are still lifted above trees/obstacles.
The second problem is that was found with Longbow radar based on the MMW which has a high resolution but from a very flat illuminating angle like in the case of hovering behind obstacles, the system has very hard problems distinguishing a source and where exactly it is. The radar waves come flat in and come flat back and the radar can not distinguish accuratley how long the tank is or might even be filtered out like the tests have shown problems with the high amount of stationary targets being seen as clutter and filtered out. While the helicopter tries to scan for the target tank a close by Shorad will immidiatley notice the radar scanning and will not have huge problems to find its prey and work against it.
Those problems are years old and have been only addressed since the Block 3 came out and to what level they have been solved is a different question, but such problems are normal to such radars especially for their purpose. The amount of clutter a sky gives is almost non existent compared what all the sources for clutter on the ground can produce and those were the results from Iraqi flat desert with low amount of objects. Europe would be a nightmare for using Radars with lot of success in this kind of setting or purpose.
Radars should always be seen as sumpliment for awarness never as a garantee or a major technology that should have highest priority for pilots and what sources of information they should trust. Military intelligence of observers and UAV's are much more useful for that role than radars, but they are just as subject to camoflauge tactics of military to hide entire weapon plattforms.