The revokex test does not work when the scratch directory is created on NFS. Given the nature of NFS, it likely can never work without looking like a security hole since O_SEARCH would rely on the server knowing that the directory did have +x at the time of open and that it's OK for it to have been revoked based on POSIX specification for O_SEARCH.
This does mean that O_SEARCH is only partially functional on NFS in general, but I suspect the execute bit getting revoked in the process is likely not common.
I'm fairly certain of the above, but I'm including Rick to confirm that this isn't something that could be made to work in a reasonably portable manner.