Is the cranial nerve blood supply encapsulated by the blood brain barrier?
I can't find a great answer to this either, but there is a known concept of a CNS-PNS transition zone, specifically as it pertains to myelination of cranial nerves. With the exception of CN 1 &amp; 2 (which are effectively wholely CNS) the other cranial nerves are anatomically similar to spinal nerves, i.e. they're myelinated by Schwann cells and have an endoneurial blood supply. But they are also myelinated by oligodendrocytes for a short distance (varies by nerve) after taking of from their CNS nuclei before reaching that transition zone. According to this paper, that transition zone should mark the end of the astrocyte coverage which is necessary for BBB function. It's not a dead-ringer of an answer but this explanation makes as good physiologic sense as anything I've seen. 

https://www.ncbi.nlm.nih.gov/pubmed/10697296