Similarly, I don't think it's really in the spirit of geocaching to log a find for a cache that you have seen, but not been able to access due to the difficulty of the terrain.
I recently found a terrain 3.5 cache that was up a tree. Not very far up, certainly not far enough to require ropes and climbing gear, but high enough to be out of reach of even the tallest person standing on the ground; and high enough to be a bit of an effort for this middle aged cacher.
I was disappointed to read the logs later and see many claimed finds along the lines of "Could not sign log due to mobility issues", "As we didn't have a ladder or small children with us we were unable to sign", "Sighted the cache but too high up to record details of visit", "Could not log as we can't reach without a ladder".
It seems to me that if you can't reach the cache, then you can't really claim to have found it as a terrain 3.5 cache. At best, you have found a hypothetical terrain 1 cache at the base of the tree.