Having walked through the terrain just north of Falaise this summer, and around Carentan two years ago, the hedge quality varies massively, as it does in the UK.
Any of you near Orpington in Kent (UK), go look at the old road running from green st green up over the hill to farnborough (called old hill, funnily enough). That old road is about 10 feet below the banks of the woods and fields either side. Follow it up to farnborough church via church road and there is a fantastic bocage on the right hand side......although they may well build on that land soon enough...sigh.
However, just as in the SE of England, a lot of hedge boundaries were lesser obstacles. Tough to get through, yes, impossible to see through, sure, but not impassable to a determined tanker. I'd say scenario designers could continue to use scattered trees for these, but for the real bocages stick woods on a road edge, with a height variance as well.
btw, those of you that want to look on google maps:
http://maps.google.co.uk/maps?f=q&hl=en&sll=51.265393,0.49386&sspn=0.068099,0.161018&q=old+hill+farnborough&ie=UTF8&z=15&ll=51.353238,0.088105&spn=0.016992,0.040255&t=k&om=1