Issues in delegating to subdomain owned by other company

[blrmaani]

I have configured my named (BIND-9) to delegate a subdomain owned by
our partner company. The queries in the subdomain are failing
intermittently.

Our partner company IT team is not ready to reveal their DNS
configuration.

When we delegate a subdomain, should the nameserver to which we
delegate
be AUTHORITATIVE?

What happens if the nameserver to which we delegate the subdomain is a
NON-AUTHORITATIVE nameserver (eg., cache-only name server ). ? Could
this be the
reason for failure?

Any comments?

Cheers
Maani