As not being mentioned in it, /hurd might be considered not
compliant to the FHS.
It is FHS compliant.
First, even if it is not the prefered solution, nothing prevents
a distributor from adding things in / that are not explicitly
described in the FHS.
It is the prefered solution.
Second, the two possible solutions for the translators in /hurd
would be /sbin (and /usr/sbin, but /usr is a symlink to /) and
/lib.
Those are not possible solutions.