Due to the number of variables which must be considered, I doubt that the question is a simple one to answer. Clearly an impact with any thicker than air obstruction between muzzle and target will have some effect on a bullet’s flight, the question is how much and at what point it matters.
The parameters influencing a bullet’s tolerance to glancing impacts is determined by: the style and construction of the bullet, its length, spin velocity, impact velocity, and the bullet's attitude in flight when it hits an obstruction. The obstruction need not be great, as a bullet in flight is affected by the impact with anything denser than air.
The bullet's style and construction, as well as its length, come into play. The stronger a bullet's construction, the less its deformed upon impact with an obstruction. A solid for example deforms less then a thin skinned varmint bullet when impact velocity and impact angle are the same. That said, the faster the bullet impacts, the greater the chance of deformation, regardless of construction or style. The more the bullet deforms, the less stable it becomes. The shorter the bullet, the more difficult it is to affect its stability by impact with an obstruction; the short bullet typically flies with less yaw than a longer bullet, so any impact with an obstruction is more likely at the front of the bullet, where an impact near the heal of the bullet more easily deflects it. A flat nosed bullet has a center of gravity closer to its dimensional center, whereas a sptizer styled bullet has a center of gravity near its heel; thus the flat nosed bullet is more stable in flight and less likely to swap ends when it encounters a denser than air obstruction. A bullet with parallel sides is less effected by glancing impacts than is a tapered bullet.
The bullet's spin velocity and its yaw are related. The faster the bullet spins, the more quickly it recovers from yaw. Typically the bullet yaws twice in flight, one upon leaving the muzzle and again when impacting a denser than air target. The faster the bullet recovers from yaw, the less deflection there will be as a result of a glancing impact with an object in front of the target.
The density of the obstruction and the angle of impact have a great effect on the bullet path. If for example the bullet hits a very dense and hard obstruction at a 9-12 degree angle, the bullet will tend to deflect (read ricochet) away from it. When shooting through brush, the angle of impact is impossible to predetermine, but it is unlikely that there is any natural obstruction short of a rock that the bullet could not defeat and continue past. If shooting prone, and your bullet impacts a rise in the ground before your target, good luck getting a good hit, or any hit for that matter.
If the point is to shoot through heavy vegetation with the least amount of disruption to the bullet’s flight, we would look for a short, flat base, nonexpanding bullet, with a wide meplat, travelling at moderate velocity, from a fast twist barrel. Now whether this combination represents the best choice for the type of hunting you do might be subject to some discussion, but at close range, where shooting through vegetation is often a problem, it would undoubtedly be the most effective.
