ISC bind is strict about CNAME of NS server:

skipping nameserver 'aa.bb.cz' because it is a CNAME, while resolving '9.4/4.3.2.1.in-addr.arpa/PTR'.

  How about Knot resolver ? 

Hello.  I believe there is neither effort to disallow them nor to make them work.  Off the top of my head I'm not sure how it will be in practice; you could just try.  Either way, please don't use them.

(I replied to the correct mailing-list.)

--Vladimir